Back to one of the original questions....
xLights, FPP, and Vixen are all separate programs by separate developers. I think I am one of a few with commit access to both xLights and FPP and probably the only person who commits to both but that is only for an occasional bugfix in xLights, my time is 99% FPP. The developers do talk though, much more closely between xLights and FPP, but we do also talk with the vixen guys as well (mainly FPP & Vixen). I believe most of the xLights guys use FPP to play their shows and the FPP guys use xLights to sequence. FPP does have an forum area where non-FPP developers can come to discuss integration, we hope to have a lot of good discussion there as we work on FPP v2.0 more in the coming months.