Saturn's icy moon Rhea has an oxygen and carbon dioxide atmosphere that is very similar to Earth's... According to new data from the Cassini probe, the moon's thin atmosphere is kept up by the constant chemical decomposition of ice water on the surface of Rhea. It's likely that Saturn's fierce magnetosphere is continually irradiating this ice water, which is what helps to maintain the atmosphere. Researchers suspect a lot of Rhea's oxygen isn't actually free right now, but is instead trapped inside Rhea's frozen oceans.I haven't read anything else about it, but I suspect it's incorrect for the link to state that humans could breathe the air, because even if the gaseous fractions were appropriate, the atmospheric pressure would probably be way too low. Nevertheless, it's an intriguing discovery.
While the presence oxygen is relatively easy to understand, the carbon dioxide is actually even more intriguing. The gas is likely created by reactions between organic molecules and oxidants down on the moon's surface. That seems rather shockingly Earth-like, or at least like the Earth of a few billion years ago.
Photo credit NASA.