I have an idea for a game meant to introduce a wide variety of systems to my regular group so we can see what kind of things we like. The idea is that the characters would be planeswalkers or possibly involved in a dream scenario like Inception; the trick is that every time they go to another world/dream/whatever, we'd be playing under a different system.
Clearly I'll want the original character sheets to be as inclusive as possible, so that I won't run into too many issues converting. For example, if I start with, say, DnD 3.5, and then they become Mortals/Hunters in White Wolf, there will be a whole bunch of skills with a big fat question mark because they simply don't exist in DnD, like Computers or Gun. (Of course, that's a bad example because I'd probably want to use D20 Modern to make the time periods match up better, but you get the idea).
What system should I look at that produce sheets that can be easiest to convert to different rule sets?
ETA: The problem I'm trying to solve with this game is the fact that my group is relatively new and we're not much liking the system we're using, so I wanted to find an interesting way to demo a bunch of varying systems to see which ones we want to try out for a longer campaign. I could just do a series of one-shot adventures, but I like the idea of linking them somehow.
Edit 2: I've been working on this some; I'm looking now at using Torchwood as my basis, since my group are all into Dr Who and the setting allows for time travel and alien tech as a plot macguffin. So I'll want something that can be stripped of setting as my "overworld" system. I'm looking at a tri-stat, a Basic Roleplaying, a FATE, a d20, and Deadlands as the "splat" systems, to cover a wide variety of systems. We're willing to dedicate some time to re-creating each character sheet before going into each session.