I've been following the GTD (Getting Things Done) method to organize my life since 2013. GTD is a method of organization and personal productivity created by David Allen (this is the book). The main objective is to “empty our minds” and have a trusted system to store and manage our actions, projects, events, goals, objectives and even life purpose.
I've just spent about a year in the following cycle: trying Nirvana, loving it, using it for a while, then looking at other productivity apps, switching to Trello then Todoist, moving back and forth, then deciding I would stick with Nirvana.
Nirvana is a cloud-based task manager that can be accessed online on any platform and has Windows, iOS and Android apps as well. There is a basic version with some limitations (like the number of projects), a complete Pro version or a Lifetime subscription (you can check their pricing here). Disclaimer: I'm not affiliated with the company in any way. It's just an app that I love!
Nirvana is made by a small independent team in Canada. So don't expect constant updates. The team is very deliberate on improvements and that makes the app extremely reliable. It brings together he GTD concepts beautifully. The developers attended the GTD Summit in 2019.