It's openshift's way of neatly packing things into one installable bundle (their technobabble) it's the way they support the various frameworks like nodejs...php and their databases. I can't say I've had much success making them, docs definitely have a learning curve. Someone else is better off describing their process, the main part is developing scripts so the cartridges communicate configuration info that's what seems to be the whole process. It's a personal preference kind of thing, you could copy/paste a git repo and it would handle itself, although I don't mind command line or shell.
Clearly though the process of getting nodeBB is a little easier on other platforms.