If you mean stuff that can run on FPGA's then https://opencores.org/
There was a student project a while ago but it was more of a proof of concept. Open source chips of any kind are few and far between, and generally not at the cutting edge, technology-wise.
Patents, as usual, will make this hard, before we even get to the economic aspects.
At my hackerspace we've been mucking about with Clifford Wolf's PicoRV Risc-V implementation on Lattice Ice40 FPGAs lately. This'll give you something that's maybe on par with a lower-end ARM Cortex-M, plus the flexibility of the few thousand spare look-up tables. All open and hackable with open source tools (except for the actual FPGAs, mind). It's not much, but it's a start.