It does exactly what it says: sells subscriptions and memberships to the users. It has a complete and through tax system, that is 100% compatible even with the overcomplicated european law.
The integrations are left to dedicated plugins, so it can be integrated with virtually any other joomla extension or 3rd party software.
It comes with a lot of ready-to-use integrations that allows you to start using it in minutes. Moreover, you can move out of popular extensions like ambra subscriptions with the 1 click importer.
Last but not the least, it's released by the most famous and trustworthy joomla extensions developer, akeebabakup.com and Nicholas. You'll find an extensive documentation and a fast and responsive support.