NodeJS steam key bulk activator. It is a tool which lets you activate multiple or single key's on steam. It includes an account manager and doesn't require a running steam instance. So you can add accounts and choose on which you want to activate a key via CLI. Because it is written in nodeJS it should be easy to implement it in other projects (I might build a webinterface).
Download all files, run npm install to download all dependencies. Then you can start via node app help and see all available commands.