Surprised my fellow typewriter folks haven't shown up yet! [paging @ebruchez]
If you want the writerdeck experience I'll echo the recommendations here for an Alphasmart. The brute-force autotyping file transfer it uses is quaint but always amusing. Gave one to a screenwriter friend and it's now gotten regular use for years. PDAs are a solid choice as well that may resonate with the HN crowd.
Don't sleep on owning an actual typewriter though. I have a small collection and use one daily. There's a rabbit hole of ~150 years of makes & models (most of which continue to function fine today) that will give any mechanical keyboard enthusiast much to chew on. :)