Tipping - Ridiculously quick tip calculator
handyCalc - Solve things in your hand.
Tip-Calculator.org - Calculate Your Tips & Split Your Bill in 2 Clicks
Calcbot for Apple Watch - Calculate, convert, and split tips from your wrist
Kickstarter - Kickstarter is the world's largest funding platform for creative projects. A home for film, music, art, theater, games, comics, design, photography, and more.
GeoGebra - GeoGebra is free and multi-platform dynamic mathematics software for learning and teaching.