The ecosystem is still young so there are not many options (great options are already mentioned for desktop)
However, there is Compose Unstyled with the purpose of being a great base for building your own design languages.
More specifically there are
platform themes that handles a lot of platform specific considerations for you (ie interaction sizing for components, font sizing depending on mobile vs desktop, non latin fonts on web, touch/click effects). There are also component primitives (unstyled components) so you don't have to build them on your own.