Small python tkinter script that tells you to get up. Just schedule it to run once an hour using your computer's task scheduler.

getup.py

#!/usr/bin/env python

from Tkinter import *
from random import shuffle

things = [
    'Make some tea',
    'Do some pushups',
    'Do some situps',
    'Go to the bathroom',
    'Go for a walk',
    'Do some leg lifts',
    'Do some crunches',
    'Do a plank'
]
shuffle(things)
text = "\nLive Longer - Time to Get Up!\n\nDo one of these things:\n\n%s\n" % (
    '\n'.join(['* %s' % thing for thing in things])
)
root = Tk()
root.geometry("320x370+270+70")
root.title("Get Up")
w = Label(
    root, text=text, justify=LEFT, padx=10, pady=10,
    relief=RAISED, bg="#fff", bd=4, font=("Arial", 16)
)
w.pack()
root.mainloop()