Thanks for your question. Here are some details regarding each of the editions you mention.
OroPlatform – The OroPlatform is a business application platform released under the MIT license. This platform is used to get a jump start on application development by providing access to things like support for SSO, workflow management, ACL’s, advanced grid and reporting features and much more. Use the OroPlatform if you are looking to develop an application of your own and want to take advantage of these features.
OroCRM Community (free for download) – Released under the OSL 3.0 license you are welcome to download and use OroCRM Community version in your business. This is typically great for small businesses or those interested in using a free community supported version of OroCRM.
OroCRM Enterprise – This version is released under our commercial open-source license or agreement. This is a paid version which include features like increased scalability, support for PostgreSQL and Elastic Search, MS Exchange support, more advanced and flexible reporting / dashboard capabilities and more. Each Enterprise license comes with support directly from OroCRM as well via our standard SLA. Enterprise is hosted on your server infrastructure on-premise or in a data-center of your choosing for maximum scalability and control.
OroCRM SaaS – Our SaaS product is the same as Enterprise except hosted in our data-centers with OroCRM managing the infrastructure.
I hope this helps and am looking forward to answering any additional questions I can. Thanks.