In an attempt to market their upcoming vampire movie, the motion picture company Sony Pictures has developed a free Half-life mod based on the movie. Underworld Bloodline is quite similar to capture the flag, but features two different races, vampires and lycans. Another differance is that you must capture a moving target instead of a static flag. Here is what is says on the official website:
Will you align yourself with the lithe and elegant Vampires, or the brutally powerful Lycans? Prowling the dark city streets and subway tunnels, you are compelled to destroy your ancient enemies while searching for The Hybrid -- a human with the power to make your people invincible.

Underworld Bloodline is a teamplay game similar to Capture the Flag, but uses a live target instead of a flag. Your goal is to find and capture the Hybrids and return them safely to a prison cell at your home base, battling any enemy fighters in your path.
A fresh breeze in the otherwise repetitive "movie-to-game" market, definately better than releasing a full price, mediocre game based on the movie, as most companies has done so far.

Source: Official site