So you're working on your project and want to see which features were not yet merged into the master branch. Do not fear, just checkout to master and run the following command:
git branch --no-merged master
And voilá! You'll have a list of which branches were not yet merged into your master. You can even create an alias:
git config --global alias.nm "branch --no-merged"
and then just run
git nm master
Hope it helps you :)