RISC-V* (Reduced Instruction Set Computing, 5th incarnation)
And sure, companies can choose not to share chip designs, but if you want an open-design CPU then you should be checking for that specifically and not just filtering by ISA. There exist such chips already, and I expect they'll catch up with AArch64 chips (in terms of being able to run desktop Linux) in <10 years, given the specs already include SIMD and the high-end chips have clock rates comparable to the oldest Windows-on-ARM laptops, like the 1st-gen Surface.
And sure, companies can choose not to share chip designs, but if you want an open-design CPU then you should be checking for that specifically and not just filtering by ISA. There exist such chips already, and I expect they'll catch up with AArch64 chips (in terms of being able to run desktop Linux) in <10 years, given the specs already include SIMD and the high-end chips have clock rates comparable to the oldest Windows-on-ARM laptops, like the 1st-gen Surface.