This tool downloads all available weapon data from the API (like this) and saves it for each patch. Every time there is a major patch, the database is updated and the changes are made available at the changes page. Each item has a CIV entry available that you can access from the stats site's page for that item. For example, this is the entry for the Orion.
This tool serves the same purpose as the in-game weapon detail tooltip that you see in the loadout menu, but has a lot more information. There are many hidden attributes to weapons including specific projectile details for lock-on rockets, as well as various attributes that are misrepresented such as headshot multiplier.
The information is compiled into a simple HTML interface for data dumping and comparison purposes. If you want a full analysis of weapon data, there is a handy tool made by Iridar that downloads the same data into an Excel spreadsheet and makes it more bearable for the average player. The CIV serves as an extension of the full stat site, it is not a standalone tool.