If you look at:
You'll see that one of the releases is not like the others. 0.27 is a
stable release, which we tested and debugged. It's the one included in
Fedora 21 Server, among other things.
If you want to package something stable, then that's the one you want.
We'll announce future stable releases here.
Cockpit development is moving very fast, and for the time being
different versions of Cockpit are not compatible with one another. If
you run Cockpit on multiple machines, and you want them to show up in
one dashboard, you should use the same version of Cockpit across all of
We're taking steps to finish and stabilize the protocol. Once that's
done we'll have the expected backwards and forwards compatibility
between different versions of Cockpit on different machines.