links and apps I might need

My classmates and the instructors have been so good at posting and suggesting useful stuff, and what happens when I no longer has access to the class? Will I lose them? Best to list them here, and always have them:

Thanks to everyone for the aid!l This will be messy as I'm just copying all the links.  And I'm putting the actual post early in the semester so it's not blocking the front page:
Links and comments from class