Ideally - Free - add, complete, view complete - lightweight - command line or web-based
Todo.txt is a thing as well. http://todotxt.org/
Taskwarrior is another. https://taskwarrior.org/
I sometimes use Whatsapp (Android) as a fast multimedia todo app. The way it works is that I create a group where I am the only member. I then add an icon on the home screen that immediately takes me to the group so I can start typing, recording voice, taking photos, etc. It doesn't have task statuses or even checkboxes, but it can manage lots of different data formats.