Hi,
I would like to propose you a simple web application development (Ruby on Rails) for this task. The main advantages of this approach would be:
1) Being me able to deploy the web app periodically online so you can have constant visibility about the progress. This is good if you spot something which should be done differently - we'll be able to find out and fix it soon.
2) When the app is done, any user will be able to connect to the application from anywhere using a web browser in order to manage his/her tasks.
3) It should be quite easy to add more functionality to the web app in case you decide to extend it later (future projects).
Please note that hosting and deployment after finishing the project is not included in the quotation. I will provide you, however, with all the necessary steps and support you'll need to do so. In any case, we can discuss this as well.
Finally, in case I've misunderstood your requirements and you prefer a single-user desktop application, that would be possible as well. The best option would be a Java desktop application (with a graphical user interface) so you could run it in any type of system (Windows / Mac / Linux).
Please let me know if you have any further questions so we can discuss it in more details.