Pop-up reminder and todo app?

Does anyone know of a reasonably lightweight app for Ubuntu that can sit in the system tray and pop up to remind me of various tasks?

Something like Kalarm is exactly what I am looking for, but on my system I seem to suffer from the bug regarding shutting down (i.e. Kalarm or perhaps nepomuk stalls the shutdown by a few minutes, and I get the report about processes still running etc). Thus, I've had to remove Kalarm and need to find an alternative.

Can anybody recommend something?

Sticky notes!

sudo add-apt-repository ppa:umang/indicator-stickynotes
sudo apt-get update
sudo apt-get install indicator-stickynotes

Hope you find it useful.

PS: You can also have: Alarm Clock — Ubuntu Apps Directory

Look at the third picture in the Store and you will see it will also satisfy your needs I hope.

There is also the default calendar in XFCE: Orage. It can be installed using:

sudo apt install orage

Once installed, the calendar user-interface is very similar to that found in Microsoft Outlook.