Invoking git instaweb spins up a lightweight HTTP server for your repository and opens it in your default browser for quick history browsing.
By default it uses gitweb and hosts on port 1234 while automatically opening your browser; you can override the web server with --httpd=<daemon> (e.g. webrick or apache2-mod_fcgi), set the listening port via --port=<port>, choose which browser to launch using --browser=<browser>, reload pages every N seconds with --refresh=<seconds>, add debugging info with --module-info, apply custom styling through --css=<url>, receive desktop notifications on reload via --notify, and control the lifecycle explicitly with --start, --stop, or --browse.
For example, run git instaweb --port=8000 to use a different port or git instaweb --httpd=webrick to switch daemons, or use --browse to only open the UI; closely related commands include git daemon for serving over the Git protocol and standalone gitweb or cgit installations for a more permanent web interface.