NOJ Desktop is a contest optimized NOJ Client supporting Windows, Mac and Linux.
See Releases page, NOJ Desktop provides binary installable files for better user experiences. It's strongly recommended to use that for participating contests.
If you want to run NOJ Desktop from source code, you need to clone it first and then run npm run start or npm run startWin after you installed all dependences via npm i.
NOJ Desktop is a contest client based on NOJ OAuth Services and NOJ Public API Services, you can use them to build your own NOJ extensional tools.