PHP5 & MySQL, with a couple of Javascript libraries for the UI and an Apache server.
No. It's completely ordinary PHP that was built on an everyday Apache server, with no special tricks.
ACH was created primarily for government clients, many of whom do not have the latest frameworks installed on their servers and will not install them for the sake of just one application. If we used a framework, a lot of government organizations would be unable to use it.
On the front end, our persistent chat room could use some work, especially in making it IE-compliant. We'd also like to beef up the matrix tables with click-and-drag resizing and Ajax-y editing.
On the back end, our .htaccess file is getting out of control with RewriteRules. We should clean it up, and that might mean modifying the links in our HTML. And there are also a few inline PHP functions and CSS, which obviously should be moved. For more details, see the issue tracker.
Github. They also host the tar file.
ACH uses a lot of tables with color-coded cells. The colors we chose don't make for the most awesome look, but we chose them specifically because they're color-blind compliant. If we chose more designer-friendly colors, about 9% of our potential user base would be out of luck.
We chose the colors simply by looking at color-blind color charts, and we haven't tested them on any humans, so if you have the ability to do this, please give us feedback.