Übersicht — Hackable desktop widgets for the Mac

OSS, free. Stumbled on it via Brett Terpstra's Time Machine widget. Bunch of directly usable widgets, but you can hack them easily yourself. Endless integrations possible. A Product Hunt widget would be the thing.

Only 4 upvotes? This beautiful widget app deserves way more attention than how it is right now, considering it was released almost 3 years ago.