Not sure which one came first, but Binder is direct descendant (down to sometimes still matching symbol names and calls) of BeOS IPC system. All the low level components (Binder, Looper, serialization model even) come from there.
From what I understand, Sun made their Doors concept public in 1993 and shipped a SpringOS beta with it in 1994, before BeOS released, but it's hard to tell if Sun inspired BeOS, or of this was a natural solution to a common problem that both teams ran into at the same time.
I'd expect convergent evolution - both BeOS team and Spring team were very well aware of issues with Mach (which nearly single-handedly coined the idea that microkernels are slow and bad) and worked to design better IPC mechanisms.
Sharing of scheduler slice is an even older idea, AFAIK, and technically something already done whenever you call a kernel (it's not a context switch to a separate process, it's a switch to different address space but running in the same scheduler thread)
Binders has been in mainline kernel for years, and some projects ended up using it, if only to emulate android environment - both anbox and its AFAIK successor Waydroid use native kernel binder to operate.
You can of course build your own use (depending on what exactly you want to do, you might end up writing your own userland instead of using androids)
As far as I understand, it is already mainlined, it's just not built by "desktop" distributions since nobody really cares - all the cool kids want dbusFactorySingletonFactoryPatternSingletons to undo 20 years of hardware performance increases instead.
Be Book, Haiku source code, and yes Android low level internals docs.
A quick look through BeOS and Android Binder-related APIs will quickly show how Android side is derived from it (through OpenBinder, which was for a time going to be used in next Palm system based on Linux, at least one of them)