Ninka is described as 'lightweight license identification tool for source code. It is sentence-based, and provides a simple way to identify open source licenses in a source code file. It is capable of identifying several dozen different licenses (and their variations)'. There are nine alternatives to Ninka for Linux, Windows, Mac and Online / Web-based. The best alternative is FOSSA, which is free. Other great apps like Ninka are ScanCode (Free, Open Source), FOSSology (Free, Open Source), Licensee (Free, Open Source) and Slic (Free, Open Source).
FOSSology is an open source license compliance software system and toolkit. As a toolkit you can run license, copyright and export control scans from the command line. As a system, a database and web ui are provided to give you a compliance workflow.