We’re building our new website in Drupal, which in turn is built in PHP. Our development machines run a mixture of Fedora and Ubuntu Linux, and we keep a collection of Macs and PCs around for testing purposes. All of our code lives in a Git repository (Check out our post on it!). We’re currently using Omega as the base theme for our heavily customized templates.
We also maintain a static asset server, which caches unchanging resources for us to speed up requests across all our other websites, at static.lanecc.net. It uses Nginx to run a private website, not exposed to the outside world. Requests over HTTP are made directly to Varnish, a fast reverse caching server, who makes them (and aggressively caches them in RAM) for you. Requests over HTTPS are made first to Pound, an HTTPS terminator, who then asks Varnish for them.