[Quoth]

In theory an epub renderer or mobi renderer will work on a 386 on DOS. If you wrote it.

Ebooks worked on Palm OS 160 x 160 screen using two different pdb formats. Calibre can convert to either pdb format. A true ebook format. Mobipocket reads either format and had one as native. It was the main ebook app on Symbian, Palm OS and Windows CE (PDAs and some phones) before 2004. I have a working Palm Z22 with Mobipocket.

There is / was also a text based web browser for DOS.

I also wrote a DOS based text editor/viewer in Modula-2 for DOS that optionally supported a Sound Blaster with its own inbuilt driver. It worked on CGA, Hercules, EGA, VGA and could edit files only limited by disk capacity, not RAM. Easily ran in < 512 K RAM. Maybe 256 K. It supported hyperlinks to same level of directory as source file.

AMB doesn't seem to offer much different to the Mobipocket pdb format on Palm OS. I forget what it was like on Symbian and Windows CE. Probably those used something closer to mobi format. Either .prc or .mobi. Amazon bought Mobipocket in 2004 and then released the Kindle in 2007. Really a mobi reader on DOS is more use, over 60,000 books on gutenberg alone.

Mobipocket supported Symbian, Windows Mobile (Windows CE), Palm OS, webOS, Java ME, BlackBerry, Psion, Kindle, iLiad and desktop windows.

I don't remember a version for actual MS-DOS.

@blazejos You'd need to write maybe two plugins.