Pistol Search serves two purposes: One, it seemed like a pretty big gap in the otherwise bounteous amount of firearm information on the internet. Two, I need to get better at JavaScript and prove to people that I actually do have an idea of what I'm doing. Employers have a tough time validating the skill level of prospective tech workers, so I thought, "Hey, I can help with this. I'll put a ton of effort into an app for the most divisive hobby in America. Let's hope for the best."
JavaScript, obviously. In particular, the AngularJS framework runs the frontend, with the (still in-progress) "material design" styling taken care of with the Angular Material library. I also use the Lodash library, at least until I feel better about using the quirkier ES6 helpers.
Right now, Protractor is the only testing tool in use, using the Jasmine test framework.