They discontinued the AlphaSmarts, but they're so beloved that there's a strong market for picking up used ones. They developed a number of models (I think initially targeting usage in schools), and the newest is the Neo2.
Writers love the distraction-free environment, and I also find it great for first drafts.
The AlphaSmart was a brand of portable, battery powered, word-processing keyboards manufactured by NEO Direct, Inc. (formerly Renaissance Learning, Inc, formerly AlphaSmart, Inc., formerly Intelligent Peripheral Devices, Inc.). Originally released in 1993, the first AlphaSmart models were intended for writing on-the-go and could be plugged into a computer to transfer saved written text.
(there are also new electronic typewriters that are trying to achieve the same thing — I’m sure you’ll find them if you google — but I’m turned off by how expensive and weirdly hipsterish they seem to be 🤷♀️)