INI (configuration format)
Plain-text configuration format: bracketed sections, key=value pairs. No official standard — just an MS-DOS-era artifact that became convention.
Classic WIN.INI/SYSTEM.INI from Windows 3.x. Dialect wars: comments with ; or #? case-sensitive? quoted strings? multi-line? Every parser interprets differently.
Lives on in systemd units, pip.conf, setup.cfg, Git's .gitconfig, MySQL's my.cnf, PHP's php.ini. Modern config formats (TOML, YAML, HCL) are successors with clearer specs.