Hello,
I did some research, these are some of the libraries
1.PHP-Auto-Update
2. This is is built for automatic updates for private and commercial plugins that are not found in the general wordpress repository but can be used outside wordpress.
http://w-shadow.com/blog/2010/09/02/automatic-updates-for-any-plugin/
Another similar one here https://github.com/YahnisElsts/plugin-update-checker
There are very good articles on exactly how wordpress automatic updates works
1.How wp auto updates works
2.wordpress automatic updates
3.Explaining wp auto updates