Agat 18 is a 35mm film half frame viewfinder camera made by MMZ and later Vilejka for MMZ (Belomo), Minsk, Belarus (in former USSR), and produced between 1984-89. АГАТ = AGAT is a special name in Russian.
The Agat 18 is a small, cheap, all plastic half frame camera of dubious quality. The glass triplet lens is actually quite sharp for such a low end camera, but the inferior (mono) coating makes it very prone to flaring. The camera is one of the smallest and definitely the lightest half frame 35mm cameras that you can buy.
There are 4 types and 5 sub-types of the camera. 
See the article Agat 18K for detailed specifications of the camera.