What are the tools and libraries that work for Gitlab ?
If you want to see packages to interfere with Git, see its own git page.
Get the list of opened issues, special commit mode
See git-commit-insert-issue, which works for Github and Gitlab (in the dev branch though). It has a commit minor mode which automatically fetches the opened issues when you type something like "Fixes #" in the commit message.
glab.el, a minuscule Gitlab library
See glab.el. It's for Emacs 25 and onwards though. It's neat on how it handles the authentication (quite transparently for the user).