Sage 300 is available in 2 options:
Sage 300
This is the classic offering of Sage 300.
It is desktop based and usually deployed as an on-premise solution.
Sage 300cloud
This is a new option from Sage that offers a full fledged solution that is both desktop as well as browser based.
As with the classic Sage 300, it is an on-premise solution, however, it is on a subscription model which makes it more affordable and accessible to smaller businesses.
Third party add-ons
Sage 300 solutions can be further enhanced and adapted by third party add-on solutions.
These are developed by Sage Endorsed Development partners. The solutions are developed within the Sage 300 SDK (Software Development Kit) and work seamlessly within Sage 300 itself.