A gear chest is an item in Evony TKR (The King's Return). It can be found after killing certain monsters or bosses, with some of them listed below.
The description of Gear Chest in Evony TKR says:
Open to receive a random Lv1 Monarch Gear.
Gear Chest is known to drop from a number of bosses or monsters upon killing, including Pumpkin Monster.
Note: This list may be incomplete.