GeoGebra: a great graphing tool
GeoGebraTube: examples of GeoGebra graphs
Latex Equation Editor:
CodeCogs you can drag and drop the image created in this app into Google docs and Smart Notebook or embed the equation in a webpage:
About Painting -- Opaque Colours : allow you to mix various proportions of primary colours
About Painting -- Water Colours : allow you to mix various proportions of primary colours