Curie is a personal trainer that will coach you to sit better. It's not about sitting straight all day but taking quick breaks and simple exercises.
Tell the app why you want to improve your posture (back pain, be taller, etc.) and it customizes a 7-day track for you consisting of short stretches you can do at your desk or at home.
The Posture Laptop Stand is designed specifically for hotdeskers - those of us who need some neck re-alignment while we work, but have to pack up and run at the end of the day! Posture is super lightweight and portable.