GitHub - Originally founded as a project to simplify sharing code, GitHub has grown into an application used by over a million people to store over two million code repositories, making GitHub the largest code host in the world.

Overleaf - The online platform for scientific writing. Overleaf is free: start writing now with one click. No sign-up required. Great on your iPad.

GitLab - Create, review and deploy code together with GitLab open source git repo management software | GitLab

TeXworks - The TeXworks project is an effort to build a simple TeX front-end program (working environment)...

BitBucket - Bitbucket is a free code hosting site for Mercurial and Git. Manage your development with a hosted wiki, issue tracker and source code.

Archimedes - Archimedes is a LaTeX and Markdown editor designed to make mathematical writing easy.