Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.
Strikethru - Strikethru is a kind of to-do list notebook for managing work lists and staying updated with the important tasks.
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.