Genode looks interesting. As far as I understand it uses the sel4 kernel? Is it really in development since 2008?

It doesn't necessarily, but it can. Genode/SculptOS is kind of a microkernel OS framework, and it can use seL4 as the kernel.

Here is a talk about that porting effort:

https://m.youtube.com/watch?v=N624i4X1UDw