Isadora is described as 'is the award winning, interactive media presentation tool that allows you to follow your artistic impulse' and is a Projection Mapping App in the Video & Movies category. There are more than 10 alternatives to Isadora for Windows, Mac, Linux and Steam. The best alternative is Pure Data, which is both free and Open Source. Other great apps like Isadora are Max/MSP (Paid), Vvvv (Free), QLab (Freemium) and TouchDesigner (Free Personal).
Pd (aka Pure Data) is a real-time graphical programming environment for audio, video, and graphical processing. It is the third major branch of the family of patcher programming languages known as Max (Max/FTS, ISPW Max, Max/MSP, jMax, etc.
Interactive visual programming environment for music, audio, and media In use for over twenty years by performers, composers, artists, scientists, teachers, and students, Max is the way to make your computer do things that reflect your individual ideas and dreams.
vvvv is a graphical programming environment for easy prototyping and development. It is designed to facilitate the handling of large media environments with physical interfaces, real-time motion graphics, audio and video that can interact with many users simultaneously.
TouchDesigner is a complete authoring tool for building interactive 3D art, visualizations, prototypes and UIs. Derivative makes and supports TouchDesigner and offers their services to do custom production using TouchDesigner.
VDMX5 was created from the ground up to meet the demands of realtime video performance. Built around a robust data processing architecture it was designed to be used with whatever hardware- or software- you've got available.