[twowheels]

EDIT 2: Does the LibbyApp.com website only allow downloading to Kindle or Libby — no .acsm downloads?[/QUOTE]

It does, but I had to search a bit for it. There's an "other options" link at the bottom of the page, de-emphasized compared to the Kindle vs Read Here options, and that allows you to then download the ACSM file.

EDIT: Interestingly it only seems to be available once, so if the first download fails you're out of luck. What a horrible UX -- it seems that they really don't want to support epub, which is weird -- isn't Libby created by Overdrive, which I thought was owned by Rakuten (Kobo).