Here is some of the software that I've written or contributed to that I think might be useful to other people. You can also check out my Github account to see many more projects.
Small Graph Database—This is a database of all 13,598 graphs with 8 or fewer vertices and various properties.
Format plugin—This is a plugin for the DokuWiki wiki (the software I used to create this website and that I'm using now in my classes). The plugin allows you to pass commands to external software and embed the resulting images in the wiki page. The nice thing about this is that you don't have to create images with other programs and then upload them to the webserver. Additionally, the changes are tracked between pages (so, for instance, you can change a graph on a page and old versions of the page will still display the old version of the graph).
Newpagetemplate Plugin—This is a plugin for the DokuWiki wiki. The plugin allows you to specify a template and also replacement variables for the template for a new page creation. The motivation behind developing this plugin was a need for a way to present a student with a way to create a homework page from a predefined template. I made it possible to have variables in the template that could be replaced with values I pass the wiki.