When you want to monitor a github repo, you can setup travis-ci, hudson or bamboo continous integration (CI) server. A problem arrises though. What if you want to run scripts on a server that is behind a firewall? The CI server may not be able to access this private server behind your protected network.
This is where gitmon is used. We can monitor the git repository for changes and then when things do change we can run a changed script. The changed script is placed within the repository itself so developers can work with it. This changed script can email people, run bash commands, whatever you want it to do.