Otter World was created with Inform and has IFID E9EFF116-5789-4A14-8EF6-B86889C82E9D. To play a work like this one, you need an interpreter program: many are available, among them Gargoyle
for Mac OS X or Windows; Windows Frotz or Windows Glulxe for Windows.
Or you can play without downloading anything by following the 'Play In-Browser'
on your web browser.