CrateDB - The Hyper-Fast Database that Truly Scales
SQL Fiddle - A tool for easy online testing and sharing of database problems and their solutions.
Arctype - Free SQL Client for developers and teams. Available for Mac, Windows, Linux, and Web.
DB Fiddle - An online tool for testing, sharing and collaborating on SQL snippets
Numeracy - A SQL pad that gives you x-ray vision for your data
db<>fiddle - An online tool for testing, demonstrating and sharing database commands and scripts.