I remember playing this Fort Wars type gamemode. Let me go into description.
You started out by going around the map and collecting crystals with a wrench, that way you could build your own base. You could create factions, and team with other people, where you'd all share crystals. It was on a block-terrain map. There were underground tunnels with super crystals, which gave you more crystals. You could use a wrench on enemies' bases and you could break into their base. You also had a repair wrench, so you could repair your blocks when someone was attacking.