TICAS

TICAS is a computational algebra system that's open source and works via a modular system. Every command is a separate .exe file, such that all of them act independently.

All these .exe files run on an adapted version of the Windows Symbol system. In fact, you don't need to download the base package to use the application, just download the module and install it.

TICAS has a powerful environment of scientific work, completely programmable. This means you don't have to use heavier programs (TICAS is pretty lightweight). Developers interested in the application can find all they need directly on it.

TICAS is a complex program, but it also hides a very user-friendly simplicity.