The problem Cheque Republic - cheque system on EVM solves

The number of use cases is unlimited like with the NFT.

You can pay to anyone who don't have ethereum address and without gas fee!

It brings known design pattern (cheques) to EVM compatible chains and it works much cheaper and faster than traditional cheques. The issuer/drawer don't pay gas for every cheque (only once for allowance)! Also it facilitates mass adotion by providing infrastructure for cheques to EVM compatible chains.

Challenges I ran into

Writing and testing secure smart contract was challenging. However with supporting community I managed to secure smart contract good enough against front-running, dobule spending, reentrance and replay attack. Writing solo was challenging.