Sentinel Application Platform (SNAP) is an open source common architecture for ESA Toolboxes ideal for the exploitation of Earth Observation data.
How to download SNAP
The latest version of the SNAP software can be downloaded here.
SNAP user manual
The official SNAP documentation can be found at step.esa.int. SNAP and Sentinel Toolboxes provide integrated help directly from the software itself. Multiple tutorials are available from here. The SNAP Developer Guide is accessible here
SNAPISTA is a GPT wrapper for Python. Its goal is to provide an easy and pythonic way to write and run SNAP graphs using Python. The documentation and installation guide are at https://snap-contrib.github.io/snapista/.