> reMarkable might do it for me if they had a more powerful CPU onboard and a way to get your code to run on it so the device can be tailored to solve more use-cases.

And there are a few app loaders/package managers that let you download new packages for it, but I agree that reMarkable isn't yet a product for your dad. Another serious product design flaw is that it does not support full disk encryption, or any encryption of documents for that matter. That means that anything uploaded to reMarkable cloud is accessible to reMarkable staff. That makes it basically unusable for work for me. It's a shame because the Screen Share (f.k.a. Live View) feature makes it a really great whiteboarding tool.

> "Feature phones" illustrated this. I wrote a few (very simple) apps for Symbian phones, and for Java Mobile Edition way back when. But there were good reasons why this never caught on and why I never bothered doing any serious development on them.

Back in the day, WhatsApp did spend the time to build a messenger app in J2ME (this was long before the Facebook acquisition), which made it possible for them to serve a very large worldwide population where smartphones hadn't penetrated. There weren't too many cheap, accessible smartphone options that had app stores or package managers available for under $500USD back then, but you could get a Motorola phone for cheap or even free from your carrier in most countries, and those supported J2ME apps. Their J2ME apps were a key (if not THE key) customer acquisition channel that got them a large underserved userbase from countries that Facebook hadn't penetrated deeply at that point. In my opinion, this non-overlapping set of users that were using WhatsApp daily was one of the reasons they were able to command a premium during acquisition. It was a hell of an increase to DAU/MAU.

In that era, per-message SMS fees, per-minute phone plans, long distance charges, and other extortionate fees were commonplace. Many WhatsApp users used it to avoid SMS/MMS charges, for which the J2ME UI was good enough to deliver tons of value, especially in low income areas.