Simple ToDo is the simplest to do list software that I have come across. You can quickly add to-do items, and assign priority to them. You can even add different colors to different tasks. And that’s pretty much all you can do with this free to-do list software.
Update (12th July, 2017): The website is not operational anymore. Alternatively, you may try these 5 Best To-Do List Software.
Simple ToDo doesn’t even needs to be installed. You just extract the binary, and run it. This also means that you can easily copy it to a flash drive, and carry it around.
Simple ToDo has a simple text based database. If you are looking for a minimalist to do list software, Simple ToDo is a good choice. However, if you want more advanced software, you can try desktop to-do list, and online to-do list software.