[frostschutz]

I already got the download working (more or less), only problem is download URLs that are not giving me a file name to work with (like mobilereads own attachmentid=30385 URLs).

Busybox wget unfortunately does not understand options like --content-disposition or --save-headers (which the real wget offers). So I might have to grab and parse headers myself using nc or whatever. Not a pretty solution.

Or I could just blindly save the file and give it a random name. Or hope it's epub and the epub contains some metadata to derive a sensible filename from.

I'll restrict downloading to SD card in any case, it's too dangerous to put random files into the internal storage (the device is known to hang on too long filenames, possibly on corrupt files too, who knows). So you'd have to put an SD card in, and create a download folder on it, for downloads to work.