From what I recall (and based on some quick retro-googling) I don't believe Foudnation was open-source. One of the complaints about it on HN back in the day was that it was closed...
You are correct, FoundationDB was free but never OSS.
You can even check the comments on the HN thread [1] when they removed the downloads.
EDIT: My bad, looks like FoundationDB wasn't fully open-source back then.