SOPMOD

SOPMOD is an accessory kit, used by USSOCOM on M4A1, FN SCAR, HK416, and other rifles. It includes sights, suppressors, grips, stocks, lasers, and even a grenade launcher. There are two kits - Block 1 and 2. Block 1 was issued from 1993, and Block 2 is issued from 2005

You've probably seen it, if you played Call of Duty 4, Rainbow Six Siege, Ghost Recon Breakpoint or even Girls' Frontline

"The mission of the SOPMOD Accessory Kit is to provide the M4A1 Carbine and SOF Combat Assault Rifle (SCAR) with the flexibility and versatility to adapt basic issue weapons to meet SOF mission-specific requirements."
-GlobalSecurity.org