For a list of non-systems software available from the servers, check here. These pages also contain links to documentation.
Only administrators are able to install software system wide. Users are allowed however to install software into their home, scratch, or data directories for individual use on any of the machines. You can install npm packages without sudo (in your home directory) by making some simple changes to the npm configuration.
This blog post sums it up nicely:
And here's the information directory from npm:
In addition you can always put in a request to have a software package installed by sending an e-mail to email@example.com