I want to know that did UI only supports the default Re-framework? Or it can support other frameworks too? Please confirm
The latest version of UiPath has other new templates also, apart from reframework. Namely, Orchestration Process, Background Process, Transactional Process, triger based attended Automations and Reframework.You can use any of these. Also, You apart from them you can create a conventional process using Sequence or Flowcharts.
In case you want to create custom activities or libraries you can do that using any .NET Language following some basic rules as mentioned here:
Let me know if any other information is required.