@shinuito already posted Sideseki, so the only thing I want to add is that I’ve found out that playing Go against people from a totally different place/style (e.g. Japan) tends to generate a totally different opening, since they seem to have a different approach to the game or to the “new openings” (I’ve marginally checked a couple of them myself, I am not much into AI stuff).
Here are three examples, where I was quite pleasantly surprised and didn’t really know what to do (lost all the first games we played btw, it took me a while to adjust to his style. We are currently at 34W-35L between us):
Opponent is always Black.
Game 1:
Game 2:
Game 3:
Game 4:
Very refreshing and fun, as you can see 
… I highly recommend joining a tournament organised by Japanese people, like this: 第５期かおり杯名人戦初中級リーグ（～3k）