Python

I used to use Dropbox for this, and it works, it's automatic, so you'll have the latest copy without manually pulling changes.

However, for any non-throwaway code i use git now. It gives me granular edit history via commits, branches for experimental changes, and i can push it to github where i can run tests and deployments for free. However if you're using git, you still need to run commit, push, pull commands but if you use an IDE or even a modern editor, it'll have hot keys for it already.

Also there are files you're not supposed to commit, like binaries and 3rd party dependencies so you may need to setup a virtualenv and run pip install on each machine independently.