a little thinking today about how people who play other games might find Adventures Dark and Deep to be useful and interesting. That led me to do a little more thinking about how we all find other games useful and interesting.
Let's face it, most of the retro-clones, retro-inspired games, and the paleo-games whence they are inspired, are probably 90% compatible, and that's a conservative estimate. I can take a module designed for AD&D and play it using the Castles and Crusades rules with little to no formal conversion worries. At most, there might be a couple of monsters or magic items that don't appear in the rules, but that's never been an issue when it comes to modules. In many cases, that's how the game itself expands its own boundaries.
The same goes for the rules themselves and the supplements to those rules. Just because the Advanced Edition Companion has the words "Labyrinth Lord" on the cover doesn't mean you couldn't turn around and use the spells, magic items, and classes it contains with Swords & Wizardry. It even goes as far as some Pathfinder products, most notably the recent GameMastery Guide, which is rules-lite enough that the information within it is a gold mine for game masters of all sorts of games.
Adventures Dark and Deep will be much the same, of course. You could take just the savant and mystic classes, plop them into your Dark Dungeons game, and move on without batting an eye. Playing AD&D but want a simpler combat system? Just drop the ADD combat system into your game and no more work required. Dislike the cavalier from AD&D? Swap out the Knight from C&C. Need a monster book that you can buy in your FLGS (or at least that's not relegated to eBay)? There's Malevolent and Benign for "First Edition", Monsters of Myth for OSRIC, the Monster and Treasure Book for Castles and Crusades, and soon there will be the Bestiary for Adventures Dark and Deep. Each and every one of those creatures would be right at home, system-wise, in any of the various retro-clones, retro-inspired games, and paleo-games.
And that's something that I've mentioned before as being an untapped source of cross-marketing. The OSR (and beyond the narrow band of players that identify with it, for that matter) is not a zero-sum game. Every book of monsters for OSRIC is a potential book of monsters for LL or S&W or LotFP:WFRP. (Gadzooks-- is there an easier way to refer to it, James? That acronym doesn't exactly roll off the ol' keyboard.) Every module for S&W is a module for LL and C&C and Dark Dungeons. It's a huge potential pot of new customers; namely, everyone who has bought or plays any other game is a potential buyer of your own game, supplement, or adventure, and it only needs to be blared from the rooftops of just how compatible they all are.
I know I'll be hitting that marketing angle hard when ADD comes out, and heartily encourage all the other publishers to do the same. Maybe it's even something TARGA could get involved in.