Refresh your posture
Limber reminds you to take frequent breaks to stretch your limbs and maintain mobility.
No chair seems to consistently produce an ideal posture  and intense static activity could cause progressive deterioration of joints, muscles, and tendon/ligament sheaths . Frequently changing your working posture, stretching your limbs and loosening your body is the current ideal method to prevent spinal health deterioration.
With a pleasant tune, Limber reminds you to take breaks to loosen up and change your static posture. Limber knows when you're not around and will automatically turn off notifications until you get back.
Source code: https://github.com/lsharir/limber
 A pilot investigation into the effects of different office chairs on spinal angles https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3326090/
 Sauter, S., et al., “Improving VDT Work: Causes and Control of Health Concerns in VDT Use” p.13-32