A fire-and-forget file sharing webapp optimized for access from the command line. Use wget or curl to upload and download files. Share with a unique URL. Files can be up to 10 gigs in size, will persist for 14 days.
A remote login utility that is mobile aware, i.e., your link can drop (say, if you're on a cellphone) and come back up later, and your session will still be running. It's kind of like GNU Screen, actually. Also allows editing of lines prior to sending with the enter key. Adapts to network latency.
A shell which acts as a better interactive Python interpreter than the standard Python environment. iPython is designed more for experimentation and playing with ideas prior to implementation than it is for actually developing code. It also supports being embedded in other software for the purpose of extensibility. It even makes it easy to prototype and test GUIs written in Python.
Hackersh is a user shell, similar to bash or ksh in how the user interacts with it. It's a front-end to lots of different security tools and lets you chain them together in the same way that you can chain regular shell commands. Requires Python and Pythonect.
A massive list of free-as-in-beer ebooks about programming: Languages, platforms, tools, and more. Ideal for teaching classes, continuing education, reference, and getting a jump start on programming in school.
jq is a command line JSON parser that implements JSONpath syntax for slicing, dicing, and querying arbitrary JSON documents. Perfect for when your favorite online JSONpath expression tester can't handle that two gigabyte JSON dump somebody just gave you to parse...