Mac-only, Windows version planned. Free to download with paid upgrades giving more features: https://tableplus.io/pricing.
Looks like a good potential alternative to https://www.sequelpro.com/ (Mac and MySQL -only, donationware).
Edit: Tried it out and it works really well from first impressions. Would definitely recommend trying it out as an alternative to pgAdmin.
sequelpro is open source: https://github.com/sequelpro/sequelpro