The main aim of the HDD-Indexer is to provide an easy to use, yet powerful and complete abstraction to the data on the disk. The main point to focus on here is that this is an external disk. It can and probably will be used on different systems. Therefore, the first requirement of whatever technology we use is that it should be cross-platform.
The first thing that comes up when someone says cross-platform is java, and for a good reason. Java has matured a great deal, and has developed into a stable language that works great across any scale. But it isn't the most easy to develop with. That honor goes to languages like python and ruby, that have a huge community of frameworks and libraries that are just ready to deploy.
Along with the language, another major aspect is the GUI. The terminal is great, but to really have a visual usability of the data, we need a GUI. While there are quite a lot of frameworks and libraries that aid in making GUI apps, the best bet is to use something that every user has installed on their system - their browser. The browser provides the ideal environment, because it is readily available and is pretty much consistent across platforms. The variations are in individual standards and procedures adopted by the different browsers, which is quite acceptable.
Deploying to a browser requires either statically compiled pages (html files) or a local web server. Static compiled pages are great, except that they cannot change, or interact with the data outside of the programmed links. A local web server is much more powerful, because it can accept requests, respond to them, and make changes (to the data on disk) as required. Python readily comes up with a nifty web server (SimpleHTTPServer) that works great for local deployment of files. But there are other powerful options that save development efforts and make deployment easier.
Web frameworks such as Django, Flask, and Pyramid allow creation of web apps while saving a great deal of developer time. Django especially has become a lot popular due to its large number of features, while Flash offers a lightweight, barebones and quick method of deploying something. I'm going to choose Django simply because I want to finish and iterate as quickly as possible. Using a local web server also (kind of) implies a local database. There's no better choice than SQLite (although there are a lot many NoSQL options coming up) to store the data on disk. At most, it should take up a few MBs worth of space.
Deploying brings up issues of dependencies. What if python is not installed? Or the libraries are not installed? And so on. To address such issues, it would be better to use a portable version of python on disk, and then download the dependencies as statically stored libraries.