It's based on the Ravnica Block from Magic, simply because the Guild structure seems pretty much tailor-made for some form of faction-based conflict, while providing a very wide range of different possible character types.
So far, I've listed the ten guilds, and worked out three different 'classes', or something like them, one each for a physical, social and magical character.
I do have some more ideas, including different races various characters could be. Some races would have to be guild specific, such as Vampires (Dimir), Angels (Boros and Orzhov) and Demons and Half-Demons (Rakdos). I realise that being too liberal with the races would lead to massively imbalanced characters, so I think that the whole thing would have to be very much role-play driven... which is a good thing, since I haven't even considered any kind of combat mechanic, or magic system. These are very rough ideas indeed.
Might I suggest the Boros could have [Embermage]s in the Magical column, and the Selesnya could have [Preacher]s in the Social column, and the Golgari could have [Rot Farmer]s in the Social column? But otherwise, this looks like it could be cool. I personally love the Ravnica setting, although I don't roleplay much. --AC
I should clarify that a lot of this is inspired by reading some of the novels based on the block. However, I will admit that I had some difficulties in the placing of certain titles. I was going to have the Selesnya social character be called 'saint', but decided against it; evangelist, though, might be fun. I do think embermage is better for boros, the labmage thing was due to a confusion between the league of wojek in particular (in which labmages are basically forensic magic users) and the legion as a whole. And yes, now you mention it, rot farmer is better for Golgari.
What sort of feel are you looking for from a system? I've [written][some] that evoke particular themes. There's always d20, Storytelling, GURPS or one of the other generic systems, of course. --Requiem
OK, I really like the idea of storytelling, but I'll admit that what little I've done is heavily influenced by the white wolf chargen systems, in particular the division into physical/social/magical (or mental, usually). In fact, for that I was thinking along the lines of prioritising tham like the white wolf systems, so a soldier would be a Boros specialising in the physical aspects, but could then specialise after that in either social or magical. I need to work on it more; some of my ideas would make it a very formal setting, with values for skills in, again, a very white wolf fashion. On the other hand, I find I do enjoy looser, less defined systems as well, so I'm not sure which way to go.
An idea I definitely want to incorporate is that a Dimir character would in fact have two characters: the real one and a cover story. This stems from the fact that, of course, there are only nine guilds on Ravnica. There are myths concerning a tenth, but they are exactly that, and only the most paranoid of individuals put any store in them. On the other hand, I think the mild suspicion every PC would encounter that another player might be an agent would be incredibly fun.