@nhl-pl sent me link to this topic. I've just tested 0.8.x branch: installation and starting up both went smooth and i could login, visit administration panel, etc...
I followed steps described here: https://github.com/ahwayakchih/openshift-nodebb, just changed 0.7.x to 0.8.x in commands.
I tested only Redis installation, no plugins yet or anything more specific yet - just visited page, looked around and logged in.
update: uploading images to topic and as category image works ok too.
Hope it helps :).
Sorry. Yes, I meant the NodeBB version. Node version is 4.2.4
After I deleted node_modules I think what happened is that npm install didnt install mongo or mongo-connect. The error was a bit vague but reinstalling those two packages resolved the problem.