T-SQUAD 3D

 
T-SQUAD 3D (short for Trojan-Squad 3D) is a first-person shooter originally released in late 1999 for DOS-based PCs, but it was only released on physical copies in a few stores, and by then ray-casting graphics were phasing out so it became obscure. Years later, it has finally been ported over to modern systems and this DOS classic is now available for free.