It doesn't appear to be open source since it's not on the authors Github. However if you're looking for a menubar app example with custom views, here is one: https://github.com/phranck/CCNStatusItem. The example in that repo is what was used for this app (presumably, since the binary in the package shows as CCNStatusItem)
I saw you got two responses, one with a custom view and one with the standard OSX implementation. So I'll throw in another one of the old standard one, that I made: https://github.com/jontelang/WakaLet