Slic is described as 'scans a codebase and identifies the license of each file. It can be extended to identify new licenses or change its detection of existing ones'. There are nine alternatives to Slic for Linux, Windows, Mac and Online / Web-based. The best alternative is FOSSA, which is free. Other great apps like Slic are ScanCode (Free, Open Source), Ninka (Free, Open Source), FOSSology (Free, Open Source) and Licensee (Free, Open Source).
Ninka is a 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).
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.