Everything here is a card — click one to open the full detail. There are three tabs: Open-source repos (what you can run yourself), Apps & websites (the paid platforms), and Terminology (the words that appear in every brief and regulation — start there if the vocabulary is new to you).
On the repos side there are 28, and you do not need all of them. Read in this order:
After that, pick by the job in front of you. Use the Purpose filter to jump to a category, and the Hardware filter to see only what your machine can actually run.