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openelec. The main problem you'll encounter is patches not applying cleanly. I rebase retroplayer on the alpha at the end of every month, and I keep an archive of every rebase. If branch "retroplayer8" or "retroplayer7" doesn't work, try using an older openelec with a lower-numbered retroplayer branch. Something will match up.
Also, on x86 platforms, make sure you install the x86 repo from the Add-on Manager. Lemme know if you run into any problems.