FOSSology
A web-based system for working through source code file by file to find out which licenses it actually carries.
HP built it in-house and released it as open source in 2007, around the time corporate lawyers were discovering that their products contained far more open source than anyone could account for. The Linux Foundation has hosted it since 2015. Scanning is done by separate agents: Nomos hunts for license phrases with regular expressions, Monk compares text against known license texts, and another picks up SPDX identifiers.
What sets it apart from a command-line tool like ScanCode is the workflow around the scan. FOSSology keeps a database and a web UI in which a reviewer confirms or corrects each finding, a process called clearing, and those decisions carry over to the next version of the same package. Results export as SPDX documents. It is heavy to deploy, and nobody has ever claimed it is fun to use.