I have just set up a webhook from our Gitlab in order to send notification on activity (git push, pull, merge requests, comments, etc). The integration script is here: https://github.com/malko/rocketchat-gitlab-hook
Unfortunately, if you mention someone in Gitlab using @user, the user does not get notified in the Rocketchat channel. This would be a really amazing integration to have working for us (and I imagine anyone else using Gitlab).
My second (less important but still useful) is as follows: our Gitlab usernames are set up slightly differently to our Rocketchat ones, so therefore a notification to @user in Gitlab might not correspond to the @user in Rocketchat. We could go any reconfigure all of our usernames in Gitlab and Rocketchat, but this isn’t ideal. If Rocketchat could provide a user alias for users (effectively multiple usernames per user) this problem would be solved. Of course, the first feature I mentioned would have to be in place for any of this to be effective anyway!