It looks similar to the AI Grenade, with a white cross at the bottom.
In Wave Mode, when thrown, the grenade explodes on impact and create a smoke screen (Blue for teammates, green for enemies). The smoke will heal players and their teammates when they stay inside it as well as poisoning enemy players. It also acts like any other Smoke Grenade, blocking everyone's view until the smoke disappears.
In Crater 2, it can be obtained through supply boxes or at the Weapon Shop (pressing F). When thrown, it will create a circle shield with many nano marks and players can get in it to heal themselves.