There are several open-source platforms and frameworks available for developing smart contracts. Some popular ones include:
Ethereum: ethereum is a decentralized blockchain platform that supports smart contract development. it offers an open-source implementation of the ethereum virtual machine (evm) and solidity programming language for writing smart contracts.
Eosio: eosio is a blockchain platform that supports smart contract development. it provides an open-source software development kit (sdk) called eosio sdk, which allows developers to write smart contracts using the c++ programming language.
It is important to research and choose the one that best suits your needs and requirements