The Psion 5mx really felt like something of the future.
I had a 5mx. Bought it for a business trip where I was making up an order from a wholesaler while examining the merchandise. Invaluable tool. Would have taken me a whole lot longer without it. Found it in storage the other day. Swapped in new batteries and turned it on and it lit up with no problems.
I had a friend who spent a year traveling around the world in the mid 2000s who said this was the absolutely perfect writing device for his blog. Nobody cares to steal it, and the fact that two AA batteries can power it for 10-20 hours means you don't have to worry about running out of electricity even in the most exotic of locations.
Check the Astro Slide. Their entire collection is inspired by the Psion (and using the same designer I think), but the Slide looks like it could be a modern replacement. I was a big fan of the Psion.