Great question — answering as the UphillTech team:
Well - you have some components on a frame which could be a bike if more parts were added. The fork lacks boots, so its newer than early 2000. But the crankset is still a triple chainring, so its not new. The stem is quite short too. I'd guess late 2000's as an age. The boxy chainstay might be a giveaway, and the downtube seems to have a fairly distinctive cross-sectional shape. Nothing here is evidence for or against "stumpjumper" All you need now is source two wheels with rotors/QR skewers/tubes and tyres, a cassette with as many cogs as the shifter has positions (one more than the number of clicks it can do), a matching chain, pedals, and a saddle+seatpost and clamp of the right diameter...
Full answer by Criggie: https://bicycles.stackexchange.com/a/97656 (CC BY-SA 4.0).
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