You slouch because you forget not to (we all do). Upright makes remembering easy, by gently reminding you every time you stay bent over for too long. It makes sitting (and standing) better, unbelievably easy.
"Learn Git Branching" is the most visual and interactive way to learn Git on the web; you'll be challenged with exciting levels, given step-by-step demonstrations of powerful features, and maybe even have a bit of fun along the way.