Akiee
Akiee is a free and open source cross-platform program for maintaining a task list with Markdown support
Kapow
Kapow – free and open source multi-platform software for time tracking
Taskcoach
Task Coach – a free, open source, cross-platform personal task manager designed for keeping track of personal tasks and to-do lists
Hamster
Hamster is a free and open source program that allows you to keep track of the time of all events of the day in Linux
KAlarm
KAlarm is a free and open source program for setting reminders, as well as for scheduling command launches and sending emails
Getting Things Gnome (GTG)
Getting Things Gnome (GTG) is a free and open source personal organizer/task manager inspired by the “Getting Things Done” (GTD) methodology
QuitCount
QuitCount – free and open source software that shows how much you extend your life and how much money you save by quitting smoking
BreakTimer
BreakTimer is a free and open source cross-platform program to remind you to take breaks, save yourself from RSI and eye strain
RSIBreak
RSIBreak is a free and open source software that periodically reminds users to take a break to prevent repetitive strain injuries (RSI)
Safe Eyes
Safe Eyes is a free and open source program for Linux users to protect against eye strain