Local IP checker / filter is a PHP program that helps to block 3rd party stat tracking when using a local network to access webpages. If you host your own website and use a 3rd party tracking company to track your visitors usage/system specs they most likely give you a piece of code to place within your HTML code.
If you dont want that code to track your visits it is pretty easy to do. This program was written with the idea that you are accessing the webpage via a local network or via the server itself (like when viewing recent updates on local production servers).
If you access the page from the LAN your usage is not tracked. If you access it via the internet the tracker code works as usual. It is fairly basic and may need a modification or two depending on your networks IP configuration.