MySQL - The world's most popular open source database
BambooHR - Personalized HR software for SMBs
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
CharlieHR - Charlie automates many of the administrative headaches you'll experience when scaling a company, so you can spend less time doing admin and more time doing the things you love.
SQLite - SQLite Home Page
Namely - Namely is the end-to-end HR, payroll, and benefits platform for growing companies.