The University now has a site license for Overleaf and you can signup for the service by going to https://www.overleaf.com/edu/princeton.
Overleaf is an online LaTeX editor that's easy to use. No installation, real-time collaboration, version control, hundreds of LaTeX templates, and more.
Overleaf has purchased ShareLaTeX and is now moving users from ShareLaTeX to Overleaf. The department will continue to have a license until summer of 2019 after that you should use the University link to sign up for an account on Overleaf.
The department has a site license to use Overleaf & ShareLaTeX, the Online LaTeX Editor. When you go to the site and signup just use your @cs.princeton.edu email address and you will get access. ShareLaTeX can be found at https://www.sharelatex.com/ and documentation is located at https://www.sharelatex.com/learn.
Princeton University Library Overleaf Announcement:
http://library.princeton.edu/news/scholarly-communication/2019-01-09/now-available-overleaf-online-collaborative-writing-tool