In addition to Open Cores, here is yet another project to build modern computer components as Open Hardware. This one, this time, is instead very much a one-man effort. This one person, however, is an academic, so it appears, so even though it is a one-man effort, it appears the project gets plenty of publicity. There is also a nice blog with plenty of information on lessons learned from this one person.
The FPGA board is an ICO board, and the name of the board mounting project for the CPU is ICOZIP.
20200727/https://github.com/ZipCPU/icozip
20200727/http://icoboard.org/
20200727/https://github.com/ZipCPU/zipcpu
20200727/http://zipcpu.com/
20200727/http://zipcpu.com/about/
This is a great article on four keys to making FPGA hardware designs that “just work.” Yes, it does hinge upon the idea of formal verification, clearly specifying the behavior in terms of “contracts,” and testing all possible code paths.
20200727/http://zipcpu.com/formal/2020/06/12/four-keys.html
This is a great article on phase-locked-loop (PLL) problems and debugging them. Clock syncing in advanced sequential logic is no joke!
20200727/http://zipcpu.com/blog/2017/09/14/even-i-get-stuck.html