way before the kindle fire you could in fact buy "active content" for kindles on the amazon storefront. I recall buying a crossword app this way. It was fine, especially since this was an original (or 2nd generation?) kindle, which still had a physical keyboard !

At some point they dumped support for this. I recall it as being around the time the Fire came out. There doesn't seem to be a lot of info left out there, e.g. it merits just an un-cited sentence in wikipedia's article on the kind. there may have been some remnants of it as late as 2020 though: https://the-digital-reader.com/amazon-removes-active-content...

It's unlikely that would have worked. 2 big ecosystems seems to be what the market will bear and choosing an Android base for the fire tablets makes a lot of sense.

Very few people are going to bother writing apps for another ecosystem. Also, more apps means less control by Amazon which won't fly