Todoist is a cross-platform to-do list app, which makes keeping track of your life (personal or professional) a breeze. Todoist offers apps for every major platform: Android, iPhone, iPad, macOS, Windows, Android Wear, Apple Watch, browser extensions, and the web.
Todoist was created by the company Doist in 2007. Doist began as a side project for its founder Amir Salihefendić. Even now, the company is completely boot-strapped (no VC funding raised), and has over 100 fully remote employees around the world. As of 2021, the company had reached $15M in annual revenue (ARR).
Mentioned in this answer

Todoist
Organize your life. Then go enjoy it.