simplewall by henry++ . written in C, size less than a megabyte
simplewall is not a control UI over Windows Firewall, and does not interact in any level with Windows Firewall. It works over Windows Filtering Platform (WFP) which is a set of API and system services that provide a platform for creating network filtering applications. Windows Filtering Platform is a development technology and not a firewall itself, but simplewall is the tool that uses this technology.