Cosmoe, a similar project that supports running Haiku apps on Linux, has also been recently revived after 18 years: https://pappp.net/?p=95060

There is also a library version where you can use the Haiku API to write Linux apps.

I do have to say... in all my years of software development, as far as system APIs go, BeOS/Haiku has by far been the most pleasant and easy-to-use API I have ever seen, so this is a very welcome addition for me.