ruby-discid
ruby-discid is a set of Ruby bindings for MusicBrainz' libdiscid.
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The latest release is: 0.1.0
There's online documentation of the (tiny) API and here's a little snippet to get you going:
require "discid"
discid = DiscID::DiscID.read("/dev/hdd")
puts discid.id
puts discid.submission_url