Instaweb is a script used to set up a temporary instance of GitWeb on a web server for browsing local repositories. Instaweb requires, at a minimum, a light-weight server such as lighttpd or webrick.
We are specifying WEBrick as the web server since it is already installed on macOS. For more configuration options see the Instaweb documentation here: https://git-scm.com/docs/git-instaweb.
Git has a built-in repository viewer for your web browser. a bit similar (but less awesome) than github.
If you have apache installed, simply go to your repository, and enter
git instaweb --httpd apache2
otherwise, simply install lighttpd and just run
git instaweb
This should open a brower automatically pointing to your repository. If not, try to connect to localhost:1234.
You can stop the server with
git instaweb --stop