Open Source Licenses
OSI
The Open Source Initiation (OSI) maintains a list of OSI-approved licenses - an authoritative list on what is considered open source.
SPDX
"The SPDX License List itself is a list of commonly found licenses and exceptions used in free and open or collaborative software, data, hardware, or documentation. The SPDX License List includes a standardized short identifier, the full name, the license text, and a canonical permanent URL for each license and exception."
Linux Foundation
The Linux Foundation provides the Open Source Licenses Best Practices quick reference guide.
GitHub
GitHub maintains the 'Choose a License' site that can help with the process of choosing a license for a project, but it is not comprehensive.
TLDRLegal
Software Licenses in Plain English
Blue Oak Council
"The Council publishes this list to identify permissive licenses, so that everyone can recognize, rely on, and use them without expensive legal help."