In the category of "Amish Computing:" Here is a very detailed review of the Quickpad Pro.
The Quickpad Pro was (is) an interesting alternative to the Neo. It runs on four AA batteries and can run DOS applications. But not all applications are guaranteed to run. It can be bought at the moment at eBay for $89.99.
It's a bit dated, having come out in 2002, I think. The domain www.quickpad.com is currently unavailable. There is a private website that has interesting information and links, including one to a Yahoo group which you have to join in order to gain access to the information. Someone complains in this group that he tried "numerous" dos editors, and that none worked. WordStar and MS-Word 5.5 can apparently be made to work.
I was half-tempted (no, more than that: I made an offer) to buy it and experiment with it in order to run Lotus Agenda, but $89.99 is too much for this experiment—at least for me—and I will not start collecting keyboards like this. They take up much more space than pencils.
P.S.: I will not, I say "not" ... collect keyboards.
1. The HP 95LX does run Agenda. See here. It can be bought more cheaply, but the keyboard is atrocious.