Mike Hoffman does some terrific stuff. His work's definitely been an influence on this new game o' mine.
I'd checked out Forbidden Kingdoms - for whatever reason, though, it just didn't particularly appeal to me. There's nothing really wrong with it, but from what I read it's more of an Indiana Jones/Tarzan pulp, and I was hoping for something with more of a sci-fi bent. Hence, development of my own homebrewed game.
To give you a flavor of it, here's some of the character classes for the game:
Gumshoes - master detectives/rogues.
Space Jockeys - spaceship/airplane pilots.
Eggheads - scientist geniuses.
Also developed a special NPC class - "cub reporter". Every group of PC adventurers needs an annoying freckle-faced kid with a nose for trouble tagging along with them.

("Golly gee, do ya s'pose pushing that big black button will do anything?")
Thinking about the d20 Modern/d20 Future situation - on second thought, I'll probably stick with d20 Modern. Most of the sci-fi stuff in this game really [u]doesn't[/u] have a basis in "real" science - part of the fun is basing everything in Star Trek-esque technobabble. Example - the spaceships that I've developed for the game are powered by devices called protonic nebulizers. I've developed rules for how they work, how they can be sabotaged, etc.; but somehow I don't think they'd be terribly plausible as rreal scientific devices. d20 Modern seems to let the game run just fine "as is", so I don't think waiting for d20 Future is necessarily going to improve anything.
I'll fill in more details as the first campaign segment ravels a little more - currently the characters are on Venus, trying to escape the clutches of the evil android queen Cleopatronica ....