While Solidity currently is the most popular language for writing Smart Contracts for the Ethereum platform there are alternative Programming Languages that can be used. One interesting option is LLL ("low level lisp like language"):

https://ecc-comp.blogspot.com/2017/12/comparing-solidity-to-lll-and-why…

https://media.consensys.net/an-introduction-to-lll-for-ethereum-smart-c…

Support for LLL unfortunately was removed from the Solidity project at the end of 2019:

https://github.com/ethereum/solidity/issues/7949