Tagging is now supported at Linux App Finder. If an app has tags associated with it, they will appear just below the program's title. Clicking a tag will display all apps that share it. A search box is also available to further narrow down the results within a specific tag.
If you are a registered user and logged in, it is very easy to add a new tag. A text box will appear just below where you can already rate the app. Type in the new tag, hit submit, and the page will reload with the new tag displayed.
Please feel free to add any pertinent tags that you think makes a program easier to find. I started adding some, but most remain untagged so far.