The BandLab website I guess it pretty similar to Soundclick/BandCAMP, in that you can upload your songs there for other people to hear.
However BandLab also have
The BandLab Editor, which is a pretty basic but fully functional DAW that runs in a browser (yes, really - this pretty much blew my mind when I first saw it).
If you use this to construct your songs, you can opt for it to be "forked" either openly to the public, or to a private group of people. You can also use this for collaboration, so that several people can work on the same song using the BandLab Editor.
This could be in the form of a virtual band spread across the globe, it could be you just want a guitar solo or vocals added, or it may be you've got a riff with nowhere to go and you're happy for someone to write something based on it.
Finally, there's Cakewalk By BandLab, which is the fully featured DAW we all used to know as Sonar.
You can export your audio stems & MIDI tracks between Sonar and the BandLab Editor so that you can collaborate on projects regardless of what DAW or operating system your collaborators are using. It does make the process easier than sharing CWP files to an extent, because if you're using audio stems it doesn't matter if you don't share the same plugins.
I hope this makes sense!
M.