Is Bitcoin Core the only protocol that uses these version numbers?
Does anyone know what ABC and Unlimited use?
Is there a place where I can see the raw version numbers for each client easily?
Bitcoin clients no longer use version 2 or version 1 in the block headers. Block version is now defined as per BIP-9, and miners use specific bits in the block version number to signal their support for specific soft-forks in the bitcoin protocol. The top 3 bits of the blocks must be 001, so the range of actually possible nVersion values is from 0x20000000 to 0x3FFFFFFF, both inclusive.