Dato is a replacement for the system menu bar clock. By default, it looks exactly the same, but when you click it, you get a small calendar, calendar events, the current time in various time zones, and more.
Shareful makes the system share menu even more useful by providing some commonly needed share services like copy, save, and open.
Lungo is a macOS app that prevents your Mac from falling asleep and your screen from dimming.
Kap is an open source macOS app I'm working on with my friends. It lets you quickly record your screen and then export to various formats and services. It supports plugins, trimming, window recording, and much more.