This is a vintage Trek 990 Singletrack mountain bike frame / frameset in excellent condition overall.  This is a nominal 18.5" frame.  I measure the seat tube at 18.5" from the center of the BB to the center of the top tube, 19.5" from the center of the bb to the top of the top tube, and the top tube at 57.5cm.  The hub spacing is 100/130mm and the bottom bracket shell width is 73mm.  The steel is True Temper Ox Comp III and the stem length is 120mm.  I am not exactly sure what year this is but it would be early-mid 1990s.  The color is kind of a titanium gray.

The frame is in excellent condition overall with only minor scuffs/scrapes here and there.  The included Aheadset headset is slightly gritty.