Mateu provides several frontends using different design systems, so you can choose he one which you like most / fits your needs. This allows you to easily create your micro frontends which you can easily embed in existing Red Hat/SAP/Oracle/Vaadin user interfaces. In the end, Mateu’s frontends are just web components which you can embed anywhere, indeed.

E.g. you can use the Redwood frontend if you want your microfrontends to be embedded in/coexist with existing Oracle UIs, or choose the SAP Fiori frontend if you want your microfrontends to be embedded in/coexist with existing SAP UIs, or choose Red Hat or Vaadin just because you like it (like I do).

I imagine I do not need to say this but, obviously, you can also serve your applications in a standalone mode without embedding them in existing Red Hat/SAP/Oracle/Vaadin web user interfaces. In fact, changing the design system for your Mateu-based UIs is as easy as just changing a maven dependency.

For some of the frontends I have used the components which are open source / free-to-use from each design system, and provided my own alternate components when the design system ones were under a restrictive licensing model, to allow you to use Mateu wherever. I will double-check before releasing the version 3 of Mateu, anyway.

SAP Fiori is a different case, and you will need a valid SAP license including SAP Fiori in case you want to use that frontend.