REUSE
The FSFE's specification for labelling every single file in a project with its copyright and license in machine-readable form.
The problem it addresses is that a LICENSE file in the repository root says very little about the file someone copied in from another project three years ago. REUSE asks for three things: every file carries SPDX-FileCopyrightText and SPDX-License-Identifier lines in its header, every license used sits in full text in a LICENSES/ directory, and files that can't hold comments – images, JSON – are described in a separate file, since version 3.2 (2024) REUSE.toml.
Free Software Foundation Europe launched the initiative in 2017. The reuse lint tool checks compliance and slots neatly into CI. A REUSE-compliant repo makes life much easier for SCA tools and SBOM generators, which no longer have to guess from the wording of a license text.