There is no lack of task management tools for Linux, but if you are looking for a simple and no-frill to-do list app, Pytask would be a good candidate.
To install Pytask in Ubuntu:
Once installed, go to Accessories -> Pytask.
Pytask is really easy to use. Click on the “+” button on the top left corner to add a new task. There is no popup window or whatsoever. You just click on the respective field and enter your task details.
When you have completed your task, you can just check the Completed box or just click the “-” button to delete the task.
Pytask comes with a very handy task search function which make it very suitable for project management. Let say that there are plenty of to-do for your current project. To search any of the task, you can use the filter to narrow down the search result. You can use any of the task field (Name, Priority, Due date, project, completed) and whether the search terms should be included/excluded in the field.
You can also add several search conditions to further narrow down the search results. There is no restriction to the number of search condition you can use, but you will usually locate the task you want by the third condition. The search result will appear as you type and there is no lag at all.
Pytask also comes with an indicator applet that can show/hide the Pytask GUI.
Pytask is lacking features like reminders, strike through for completed tasks, and many other stuff, but it is never mind to be a full-featured tool. For a simple task management tool, it has definitely done its job well. And yes, it is lightweight and run blazingly fast. Do give it a try and let us know if it is your piece of cake.