So I don't think I should actually touch the game I am about to present to you with anything but a 10 ft pole, but well... it is probably a damn fun game ;)
Anyways...Wagic is obviously an only half-heartily hidden Magic the Gathering implementation on your favorite gaming device (including the neat Linux driven N900, which is actually a FOSS dream compared to all those Android smart phones... no, I am not getting paid for mentioning it ;) ). And with that we have already the main problem with Wagic... it's data and media can obviously not be really free, even if they don't actually use any copyrighted pictures from that game as far as I can tell.
But the rest of that game looks actually really nice, and with the source under the BSD you can't make much wrong, right?
But maybe the engine could be combined with the really FOSS Wtactics card game? (Edit: yay, they seem to consider doing so in the future; see comments!)