Any local machine may be problematic (if you have a dynamic IP), but git is really easy to host on a VPS or any box with a static IP -- just make sure you have everyone's SSH keys authorized (not on root unless you trust everyone with that), and use the following:

    $ git remote add origin2 user@your-ip:/path/to/repo.git

To create repo.git:

    $ mkdir repo.git  
    $ cd repo.git  
    $ git --bare init

Email.

No seriously, that is the simplest thing to use and punches right through any firewall, anywhere. Instead of git push, do this:

    tar cvf project.tgz .git
    mail -a project.tgz [email protected]

    Subject: Pull request #9042
    Please pull master branch from attached
    git repository, it fixes all the things.
    ^D

The other end can extract that and add the remote pointing to the local filesystem path.

Other than that, any file server will work. Apache, nginx, samba (just mount it), rsync, even *ftpd.

While not as nice as hg serve, there's git daemon.

If your team is small enough, why not use bitbucket as a remote as a backup option?

gitolite