I don't want to put you off your project, but Gemp is actually a pretty solid platform. The developer is still around, even though he's not been that active this year, so it's still possible that he will return to do some bug fixing, he implemented a new league type to the website only a couple of weeks ago. The existing bugs are fairly minor, I pretty much always find when something goes awry that it's me making the mistake, not the program. I can understand why some might find the interface ugly, but it's a card game, and I think graphics aside from the cards themselves are a low priority.
Of course, if you're doing this for fun, then don't let me dissuade you

But personally I am a big fan of Gemp. I believe there is, or at least was, another platform called GCCG, but I have no idea whether it's still active, having never played on it myself.