Saas (software as a service) means that amacus can be used by anyone anywhere with a computer that has an internet connection. It's hosted online and you get to it with a web browser so there's no server to maintain, no firewall that needs to be poked through, no IT group to bug for access.
Amacus is an online, monthly subscription service with no requirement for long term contracts. If you determine that it's not making you money, you're not locked in. Simply cancel your subscription.