UPDATE:According to an user comment below in this page, Ace of Spades is no more free, it is now a commercial game. However there is a free version named Build and Shoot based on the same engine..

Here is the link to Build and Shoot

Ace of Spades is the best bits of Minecraft crossed with the fast-paced shooter gameplay of Team Fortress. Free and runs on any PC.

Link to Official Site

-Build anything – defensive positions to fortresses
-Destroy enemy structures, dropping opponents to their death
-Use your spade to dig through terrain – make trenches or tunnels
-Massive maps with lakes, rivers and tunnels
-Realistic rifle, shotgun and SMG including ironsights and recoil
-Dynamic lighting system based on ambient occlusion
-Up to 32 players battling simultaneously
-CTF or Territory Control game modes