(This is basically just me geeking out, which is why it's not part of my regularly scheduled posting).
I just made an interesting realization about Cubicle 7, one of the hottest up-and-coming game publishers. The secret to their up-and-coming-ness is that they don't have a house system.
Now, a little background: Most RPG publishers have what is known as a "house system." That is, a ruleset that is used for most, if not all, of their games. This has a number of advantages.
For one thing, it saves a lot of effort in making games. The basic rules already exist, so you can focus on things that make a given property or setting unique. Magic spells, elves and dwarves for a fantasy world. Spaceships and laser guns for a science fiction setting.
You also have the advantage that some players will already know the rules. If they bought your horror game, they already know the basic rules behind your steampunk game and are more likely to buy it.
The downside is that not all systems represent all settings equally well. If your system is tuned towards gritty realism, it's going to fail at representing a world of whimsical fantasy.
Cubicle 7 has managed to acquire all the benefits of using a house system and dodge the downside. How did they do this? By licensing other game systems.
Doctor Who: Adventures in Time and Space uses Eden Studios' Unisystem, which was used in such popular games as the Buffy The Vampire Slayer RPG and Witchcraft. Just a few tweaks to the existing engine and you have a system that does Doctor Who very well, I'm told.
Starblazer Adventures is based on the Starblazer comics and uses Evil Hat's FATE system (the same one used in Spirit of the Century) to represent a much more two-fisted "rock and roll" ruleset than Unisystem was.
When Cubicle 7 announced that they were doing a game based on Charles Stross' Laundry series, they also announced that they were using Chaosium's Basic Role Playing system, most famous as the rules behind the Lovecraftian horror RPG Call of Cthulhu. The amount of potential (and very easy) cross-pollination is simply staggering.
So Cubicle 7 continues to beat the house. Good luck to them.