Have you considered just using a Webapp? Take Wunderlist - you can turn on desktop alerts (I can only confirm for Chrome).
Wunderlist is the easiest way to get stuff done. Whether you’re
planning a holiday, sharing a shopping list with a partner or managing
multiple work projects, Wunderlist is here to help you tick off all
your personal and professional to-dos.
Doesn't get much simpler than this!
Here is a screenshot of the reminder (when used in Chrome) - click anywhere on this and the task will open in the browser. This will pop up, and then about 20/30 seconds later there will be a little chiming noise to alert you. Not too sure why there's the delay...
This is turned on by going
Account Settings >
Notifications then turn on
Push Notifications and
Desktop Notifications - I'm not sure which of the two it is, so I have both on just in case! Also make sure that Chrome is allowing notifications.
They also have apps for every platform under the sun:
- Windows 7/8/10
- Mac OS X
- Android Phone & Tablet
- Web App
- Windows Phone
- Blackberry (Apk for Android)
- Browser Extension for Chrome, Safari & Firefox