QOwnNotes is a plain-text file notepad and todo-list manager with Markdown support and Nextcloud / ownCloud integration.
Taskwarrior is Free and Open Source Software that manages your TODO list from the command line.
It is flexible, fast, and unobtrusive. It does its job then gets out of your way.
a to do list to get your head free.
Super Productivity is an advanced todo list app with integrated Timeboxing and time tracking capabilities. It also comes with integrations for Jira, Gitlab, GitHub and Open Project.