Hi,
First of all you can filter the Forge on application type, all components shown when filtering on Reactive are compatible to be used in your reactive applications.

To help yourself deciding, remember that reactive web app is passed on mostly the same technology also used by mobile apps.
Rendering your UI takes place by reactjs in the browser NOT on the server like it does for traditional web applications.
So following will NOT be compatible
- OutSystems UI Web theme and patterns or any components based on them
- SilkUI Web theme and patterns or any components based on them.
What wll be compatible are components that have pure server side logic or data elemrnt, server actions, structures, entities.
What most likely will be compatible or could be made compatible are OutSystems UI mobile components that do not used local storage, offline sync logic and Cordova plugins.
Regards,
Daniel