This application is free and run on Linux.
APT-GET: sudo apt-get install cheese
sudo add-apt-repository ppa:dhor/myway
sudo apt-get update
sudo apt-get install rawtherapee
NotifyMe is especially useful for busy people who use computers heavily as part of their daily lives. When time is getting away from you and standard reminder programs just wont do because their messages are too passive (i.e. you don't notice them) then NotifyMe is for you.
You can make NotifyMe loud and very obvious, so you never miss your reminders.