openHAB 2 is indeed in beta. I believe your guess is correct, the “beta” repo is the nightlies or at least pretty recent and the stable is the Beta Release 3 version from a couple of weeks ago.
Once OH 2 is fully released this will change and the stable will be the most recent full release and the beta channel will be for the next version currently under test.
Actually upon further looking I think I’m mistaken. The Stable directories are currently not populated and the Beta only has the current stable release which is beta3. Once OH 2 goes to a full release the stable directories will become populated and the beta directories will be for testing the next release.
If you want the nightlies you need to download them from cloudbees.
deb http://dl.bintray.com/openhab/apt-repo2 testing main
will not get updated until OH2 b4? Any timeframe for this?
And to switch to nightly builds all is needed - edit the /etc/apt/sources.list.d/openhab.list
substitutuing bintray repo for cloudbees and than running