I'll definitely be checking that out, but the Arduino software platform has been the real winner and there's no question about its openness - their bootloader, IDE and libraries have all done very well in the community. They've even got tools to make pulling in external libraries super simple, I'll have to check out PlatformIO and compare.
PlatformIO is even simpler, you just add your libraries and versions to your config file and it pulls them in automatically, plus it autoupdates your platforms so you don't have to. I love it.