HCS is the only major combat system to never have been used in any sim. It was the successor to DCS. It featured a sophisticated graphic HUD with moving bars for health, stamina, and armor; and rezzable health packs which could be dropped on the ground and then ran through with your avatar to pick up the extra health. Unfortunately for HCS, it was released at a time when RCS was achieving its peak popularity, and therefore it never gained much footing in the market.
HCS is still sold at Gistya's Evil Base.