Well, I see you already got some answers on another forum, but I’m going to write an essay anyway, both for the sake of giving you my overview, and for anyone else who’s interested.
Of course, when I was 90% finished this I came across the following article, which gives more detailed overviews of several and has nice pretty pictures of the covers, next to the covers of the originals!
http://totheblogmobile.com/2009/05/08/a-guide-to-retro-clone-roleplaying-games/
Short answers to your questions
Compatibility? 90%+ of the retro-clones are very closely compatible with 1st ed or 2nd ed
AD&D. The changes in the rules are mostly not that radical. In part due to the confusing multiplicity of basic D&D sets in the 70s and 80s, many, many gamers freely mixed the different official versions anyway, which were just as compatible/incompatible with one another as any of them are with pretty much any of the retroclones.
Advantages over AD&D? First, they’re in print/easy to get copies of, at least in PDF. Some
OOP D&D or
AD&D editions / volumes are easy to find. Others difficult and expensive. Second, pretty much all of the retroclones are better edited and explained than 1st ed
AD&D. The original
AD&D had multiple rules sections which were a tangled mess. Ranging from basic stuff like initiative & unarmed combat, to less-necessary subsystems like psionics. You think people argue over
GW games? Hah! You should SEE the initiative and alignment argument threads on an old-D&D forum. Or read them in old issues of Dragon. Many of the same arguments have literally been going on for thirty plus years, and the internet lets them get even deeper, pickier, and more arcane! That said, if you and your group are grownups and don’t mind investing a little time, you can certainly hash out house rules which make
AD&D perfectly playable. And of course, if you find an existing group the
DM has already done this. Then it’s just a matter of learning the house rules. And of course, 2nd ed largely cleans up 1st ed and makes it significantly easier to understand, though it does change a fair bit.
Longer stuff about retroclones in general
Each of the open license “retroclones” is written to meet its publisher’s/writer’s particular preferences/objectives. Which vary a bit.
The original point of them, from what I can tell, seems to have been to have functional “clones’ (as identical as legally-possible) copies of out of print games available online, so that anyone who wanted to play those out of print games but couldn’t get copies could use the clones. ALSO so that people could legally publish NEW materials (like modules) for the old systems, by writing them for the clones.
The basic legal bases/rationales people are doing these on actually vary a little as well. Some folks are publishing under the OGL, which is WotC’s open license. Technically this license applies to the 3rd edition rules, but some of the writers/publishers argue that their retro-clones are actually just extrapolations from/extensive modifications of the 3rd ed rules, at least for legal purposes. Other publishers/writers are working on the basis that under US copyright laws you can’t patent/copyright game rules; only the unique expression thereof. So as long as they don’t copy the exact text/tables of an existing game, they are free to publish the same rules, expressed with different phrasing & presentation. Some of the writers/publishers have also chosen to make additional tweaks to the rules they’re replicating, either out of personal preference or to lessen similarity/replication of some idiosyncratic part of the original which might constitute a unique artistic expression.
From what I can see part of the original movement was also to make the retrogames available for free, both in the interests of expanding the movement (minimizing barriers to new players accessing the rules), and to minimize any risk of legal trouble from WotC. However, some of the folks doing this have also wanted to recoup expenses and/or clear an actual profit from their work, so the “free” part isn’t universally true. In some cases, the core rules are available for free (maybe the PDF free and a printed version sold, as printing costs money), and the modules or supplements are sold.
As far as individual games go, there are quite a few now, but here are some I know a little bit about:
OSRIC: I think this is the granddaddy; may be the original project. This is a functional duplicate of 1st ed
AD&D. That said, they did have to make some editorial changes because the original 1E rules are kind of a mess. The Initiative rules, for example, are incomplete and partially explained in three different places. So the guys putting OSRIC together had to clean them up, which inevitably means making some changes/clarifications, which may result in those sections looking different from what a given person remembers playing, which were likely house rules/simplifications of the original mess. To the best of my knowledge OSRIC is free, but you can buy a print version.
Labyrinth Lord: This is an almost-exact duplicate of the 1981-era “B/X” rules (see below). The publisher/editor/writer has made a few tweaks both out of preference (like giving Clerics a spell at 1st level), and (from what I understand) to avoid duplicating unique expressions/idiosyncracies in the original rules which might make a more compelling copyright case. For example, some of the experience tables or save progression tables,
IIRC, originally had progressions which did not follow any mathematical formula, so for
LL he rationalized those progressions. I like this one a lot, and it’s the only retroclone I own so far. Labyrinth Lord also has two expansions- “Original Edition Characters” and “Advanced Edition Characters”, which tweak the rules to make
LL work more like
OD&D or
AD&D, respectively.
Basic Fantasy Roleplaying Game (aka BFRPG): Another clone of B/X, but with a bit more tweaking, including ascending armor class and separation of Race and Class, which is usually one of the major features of old D&D as opposed to
AD&D.
Swords & Wizardry: Basically a clone of
OD&D (below), with two versions, one a bit expanded, the other (White Box Edition, as
OD&D at one point was sold in a white box) more minimalist & closer to the original.
Castles & Crusades: Castles & Crusades is more or less a new game which straddles the line midway between 1E
AD&D and 3rd edition. It adopts a lot of concepts and aspects of the rules which are clarified & standardized in the 3.x-era /
D20 system generic rules, but sticks primarily to options (in characters, spells, monsters, etc.) which are covered in 1st edition. It also has its own custom non-combat task resolution system called SIEGE, in place of a skill or proficiency system. This one has a mixed reputation in old-school circles. A lot of folks like it, because it captures the feel of 1E pretty well, because the publisher Troll Lord Games has been successful getting it into bookstores, and because Gary Gygax published some stuff for it in the years before he passed.
OTOH some folks dislike it because it’s mechanically closer to 3rd ed, because the art & design are newer-school, and because they prefer the original games and don’t want C&C replacing them, even if it is a “living” system. That’s my perception, anyway.
Microlite74: A tweak to Microlite20 to hew closer to
OD&D. Microlite20, in turn, is a super-trimmed-down minimalist adaptation of the 3rd edition SRD (System Reference Document), the free online version of the 3E & 3.5E rules WotC makes available.
Ruins & Ronin: Swords & Wizardry, but re-flavored for a movie-version of Japanese-flavored fantasy which has about as much historical accuracy as
OD&D does for medieval European history.
Mazes & Minotaurs: Straddles the line between original and clone, this is a “what-if” game, basically answering the question “what if
OD&D hadn’t had medieval and Tolkien elements, but was purely based on Classical mythology & legend?”.
Capsule guide to out of print D&D versions:
As far as different official versions of D&D go, remember that following Gygax and Arneson’s legal disputes in the 70s, TSR split the “Dungeons & Dragons” and “Advanced Dungeons & Dragons” brands, and Gygax firmly maintained that they were two totally distinct games, despite the obvious silliness of that idea. It starts with Dungeons & Dragons (aka “original D&D” aka “
OD&D”, aka “the little brown books” aka “LBB”), published ~1973 or 1974. Then the legal disputes which split the brands, so you get two separate development tracks.
AD&D:
AD&D came out in hardcovers in 1978-1979, starting with the Monster Manual, which was actually directly compatible and immediately-usable with
OD&D, partly designed to give the company a quick infusion of cash as publishing these hardcovers was a huge investment that they didn’t know would pay off as well as it did.
AD&D begat 2nd edition
AD&D in 1989. People also informally refer to Unearthed Arcana (and the Dungeoneer’s and Wilderness Survival Guides, which introduced non-weapon proficiencies) as “1.5 edition” as it has a bunch of new rules and indicates a bit of a shift in direction. And 2nd ed had the “Players Option” books published in the early-mid 90s, which gave a bunch more new options & tweaks, and these are sometimes nicknamed “2.5 edition”.
D&D:
Next after
OD&D there was a monochromatic (blue-toned)-covered D&D boxed set, edited by John Eric Holmes, which cleaned up a lot of
OD&D, and was developed at the same time as
AD&D (published 1979, I think?) so has some unique idiosyncracies and references to
AD&D. It only goes up to level 3 for adventurers and seems in some way to be designed as an intro product for
AD&D. The main nickname for this is just “Holmes”, or “Holmes D&D”.
Then in 1981 came the Tom Moldvay-edited Basic D&D boxed set, with a mauve or red cover, and its expansion the David Cook-edited Expert Set (with a blue cover). This is a clearer, cleaner, more standardized version, and got a lot of players into the game.
In 1983 Gygaz had Frank Mentzer re-do the latter project, with even better and cleaner editing, slick Larry Elmore art, great introductory adventures, (etc.) as the perfect introduction to D&D. This version had five color-coded boxed sets (red Basic, blue Expert, aqua Companion, black Master, and tan Immortals), covering levels 1-36, then Immortality afterward. Mentzer’s version is commonly nicknamed BECMI, making the titles of the sets into an acronym. It’s also sometimes refered to as “Mentzer editition”. Mentzer red box basic is possibly the best selling D&D version ever, and got literally millions of people started. Including me.
~1990 was the final gasp of old-school D&D, when TSR published the Dungeons & Dragons Rules Cyclopedia, which basically assembled the first four Mentzer sets (BECM), and added a couple of expanded things, like a new unique set of rules for Skills.
3.x (3rd ed & 3.5):
In 2000 Wizards re-launched D&D, rationalizing and standardizing most of the mechanics (many around a “roll a
D20 and hope for high” core), and trying to fix as much as possible that frustrated people about D&D, while keeping the original purpose and feel. This was massively successful on the whole, getting a lot of people in, or back in. But it definitely alienated a lot of people who still love the old stuff, which is really is not directly compatible. Anyway, there’s a shedload of stuff that could be written about 3rd ed, and its impact on D&D as a whole, and how old-schoolers feel about it, and its changing place in the picture now that
IT is out of print and supplanted by the even-more-radical redesign of 4th ed, but I don’t have the energy or interest to even start that right now.
