“GeoGebra is dynamic mathematics software for all levels of education that brings together geometry, algebra, spreadsheets, graphing, statistics and calculus”.
Open source. Works online, on the desktop, and as an app.
This software is useful for creating your own objects to achieve a better understanding of mathematical concepts.
Example: Coordinate Geometry
Example: from the tutorial Basic Geometry Constructions
Example: from the tutorial Algebraic Input, Commands and Functions