Gogs

See also: looks like it's been forked, so use Gitea instead.

Get the packager.io auto-build package repository and install gogs:

apt-get install gogs

Point nginx at it:

server {
   listen        yourip:80;
   access_log    /var/log/gogs/access.log;
   error_log     /var/log/gogs/error.log;
   server_name   git.youroutfit.com;

   proxy_set_header X-Real-IP  $remote_addr;
   location / {
      proxy_pass http://localhost:3000;
   }
}

Then set it up with a PostgreSQL database (or MySQL if you have to) and whatever else, have a look at the configuration docs for reference:

sudo vi /etc/gogs/conf/app.ini