Geogebra is dynamic mathematics software that combines geometry, algebra, spreadsheets, graphics, statistics, and calculus. It has millions of users around the world and is available in many languages. Geogebra allows for the creation of interactive learning materials and is open source for non-commercial use. The document discusses how technology can be used as an amplifier to help transcend limitations, or as a reorganizer of mental activity, and the distinction between exploratory versus expressive student activity when using dynamic worksheets in Geogebra.