At the other end of the scale, if anyone wants to play you can run a little openpower CPU on an FPGA with completely open source. https://github.com/antonblanchard/microwatt

It's capable of running Linux, some example docs are https://shenki.github.io/boot-linux-on-microwatt/ The toolchain consists of "apt install gcc-powerpc64le-linux-gnu" on Debian, no funny downloads. And if you want to target a Lattice ECP5 board even the FPGA tools are also all open, thanks to Yosys and friends.

All the openpower ISA spec PDFs are available for perusing on the openpower site.