Historically, some cameras, such as view cameras, or TLRs, did use a ground glass screen, rather than an eye-level viewfinder for the photographer to compose/focus. However, in the case of the view camera (the kind with a bellows, with no mirror in the body), the image on the ground glass would be inverted top-to-bottom and left-to-right. TLR waist-level viewfinders (where a single mirror is used), reverse the scene left-to-right. Correcting these reversals is the entire point of the pentaprism/pentamirror in a dSLR viewfinder.
Very few digital cameras would have anything like that these days, because of the LCD screen on the back of the camera taking their place. Flip-up or twist-out varieties of LCD screens also allow for waist-level shooting, but with better framing accuracy, and no L-to-R or top-to-bottom reversal of the image you see. And with digital data, there are a lot of additional advantages with features like magnification, exposure simulation, and focus peaking that you can never do with an optical viewfinder.
See also: Is waist level photography with a digital camera practical?