I had the chance to interview Eric Schlaepfer about his MOnSter 6502, a 6502 processor made out of discrete transistors.
For me, one of the most interesting things about this project are the similarities to ASIC design, for example Eric wrote his own LVS tool.
You can find out lots more at his website.
Here’s the visual 6502 simulator.
You can also hear other interviews with Eric over at The Amp Hour and The unnamed reverse engineering podcasts.