ToDoList is Free Open Source Software (FOSS) written in C++, see CodeProject article.
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Pro Great functionality, lots of options
Cost, percent done, priority, you name it - you have it. If you prefer simple layout - no problem. You can configure everything.
Pro Configurable calendar view, day view, Gantt chart, Kanban
Plugins available for e.g. Kanban and MindMap.
Pro Comments with richtext format
It means comments can have different fonts, links to the pages or links to another tasks. You can format text your way.
Pro All features are free
Unlike many other to-do applications that have pricing plans to unlock additional features, all the features here are available for free.
Pro Multi-level subtasks
Pro Portable & lightweight
Default portable is 2.5 MB.
Pro You can set as many filters as many columns you have, as well as export your view or single tasks
Pro Dummy content (optional) included
Makes it easy to comprehend most features.
Pro Multi criteria sorting
Allows for sorting by 3 criteria. Missing in most task management apps.
Con Windows version startup too slow, on 1st time use
8G RAM, SSD, ToDoList Starting always takes 3-5 seconds to load, but if you go to settings and tune it to start with Windows and to minimize instead of closing, it will be instantaneous next time you use it.
Con Android app is in early stages still
Only the Windows version is fully-featured. The Android app is still in early development.