An excellent blog post on how Wordpress backdoors work, how they're hidden, and how they're used.
Just like in the movies, type random keys into this web app and it'll print nifty-keen-like-wow source code onto the screen.
A Subversion tutorial written for software developers and not sysadmins or repository maintainers. Teaches you what you need to know in order to get work done.
The archive of 80's and 90's computer magazines of all sorts and kinds, brought to you by archive.org. Including some you've probably never heard of but might want to peruse out of curiosity or a sense of nostalgia.
Paste in HTML, CSS, or JavaScript, hit "Clean", and it'll clean up whatever you gave it so that it's more readable.
A framework for building cryptographic protocols so you don't have to do it from the ground up. Mutual and optional authentication. Multiple languages supported.
A website that demonstrates the important bits of HTTP as a protocol. Also has some online tools incorporated (current IP address, stuff like that). Great for testing your own HTTP interaction code.
A wiki of resources for people writing bots - actual bots to interact with, tools, tutorials, code, and datasets. exocortex chatbots howto twitter
The github repo of security features that should be built into webapps during development.
An online collaborative editor that uses Markdown natively for hacking code.