There are websites that allow one to work on LaTeX documents collaboratively, much like Google Docs. They also keep the files on their servers, so you can access them from any computer. All have free and paid plans.
- ShareLaTeX
- Overleaf
- Authorea
- TeXeR, for single equations and ad hoc usage, this site will typeset fragments of LaTeX into images, MathJaX, or PDFs. Great for trying out new commands.
If you know of any other sites, please feel free to send me an email.