Oh shoot, you want a L1 blockchain, nvm the above, those are for decentralzed apps running on the Ethereum blockchain
Just go on github and fork bitcoin
Charlie Lee forked it in one night and created Litecoin
Many forks of bitcoin
You can also fork other blockchains, like Monero
You can fork Ethereum, too
I believe the language for bitcoin is C++ but I could be wrong
Ethereum may use another language
I think Tezos uses Ocaml or some thing like that. Possibly Cardano too. Best to go on their github
Tezos moved to Gitlab
The key is that they are all open source projects
Good luck!