The term Podio books is a verbal play on audio books. Generally Podio books involve authors reading their own work and serializing it as Podcasts. This is still a fairly new form but there's already some very good work out there. Many of these can be found at Podiobooks.com.
My personal favorite Podcast fiction so far is Heaven by Mur Lafferty. Lafferty is an early podcasting hero with a number of other podcasts under her belt. Her vocal personality is engaging and the pacing of the story of Heaven is perfect for this medium (though some wise publisher ought to be encouraging her to adapt it for print!). Without giving too much away: it involves adventures in the afterlife, lots of mythology, friendship and romance and the apocalypse! The closest comparison I can make is that it reminds me of the best of Neil Gaiman's Sandman. (You can also watch lots of Mur at Lulu.tv--giving away the truth about history.)
Other Podio fiction that might be of interest includes: James Patrick Kelly reading his Nebula award winning novella Burn. Jack Wakes Up is a noirish mystery novel featuring a washed up movie star. Grey by Jon Armstrong is an intriguing novel of a twisted near future. Escape Pod is a long running anthology of audio short science fiction stories: a great backlog of listening pleasure.
There's much more in the Podioverse. I've only begun to explore what's out there, but I've already found lots of good stuff. It's all free (I do all my subscribing through iTunes) and a great way to try out different authors and find new things that you might like. It provides me with tons of stuff to listen to in the car or when I'm doing chores around the house.