A rudimentary stock certificate system that basically turn stock into NFT, but with milti-signature system (i.e. board). This is so that every transaction is traceable and solve the problems of over-issuing, etc.
Every company's NFT can be viewed on Opensea and each company will have its own Opensea collection.
Just put it on Remix and compile StockSystem.sol, and use Remix as the interface to this contract.
You can first createCompany and it will give you its token_id.
You can attempt to issue stocks by issueStock, but this can only be done by board members, and it will need some fixed amount of board members' confirmation. After calling issueStock, you will get a tx_id. Give tx_id to other board members and let them do confirmTransaction. Once enough board members had confirmed, the stock will be issued to the original caller of issueStock.
You can now freely transfer your stock via Opensea, the contract that made the NFT, or StockSystem's transferStock. You can also see that all the stock issued by the same company will be under one Opensea collection, with the company's name as its name.
You can do stockRedemption to redempt your stock, but the actual money transaction isn't covered by this system. Contact the company directly after you redempt your stock.