LibrePilot and OpenPilot projects split about a year ago when a lot (most?) of long time devs decided they didn't like the OpenPilot politics and went their own way thus forming LibrePilot.
The old OpenPilot tried to take a new direction under a name OPNG, slowly killing off (first the wiki servers and then eventually forum servrs got shut down) the original OpenPilot, but OPNG also slowly died.
There was also some bad politics back in I think 2012 where some OpenPilot devs decided to fork OpenPilot, creating TauLabs, which also seems to be doing just fine.
So yes, you could say LibrePilot is a continuation of OpenPilot
APM and Ardupilot are completely different projects.