Does reward point redemption count as "free"?
If so, the Viggle store is a new option, but an interesting one. I've been using their iOS app for a while, since it's a fairly easy way to rack up points that would hopefully be good for something (aside from saving up 2M points for an iPad Air).
Viggle gives 1 pt/min for checking into a TV show, from the time you check in until either you check into a new show or that one ends. Some shows have live trivia games, where answering questions while watching the show during broadcast (instead of DVR) scores more points - the Grammys had a 250/question game, and The Flash had a 100/question game plus a 4x bonus point rate for the basic check-in. (That is, check in for 60 minutes and get 180 bonus points.) The other big point options are watching ads (usually 20 points and 15-30 seconds each) and matching songs (100 points each, max 20/day, no points for repeats). I usually check into whatever I'm watching, zip through the music-only channels to match 20 songs a night, and play muted ads when I'm not busy - which is worth about 2500 points a night. I think the usual maximum is 6000-8000 points per day, which resets at midnight Pacific time.
So much for the points economy. I was originally into it for B&N gift cards (Nook books!), but those dried up last year. Now Viggle has their own online rewards store, which started with music and has since added movies (some of which are UV-compatible) and - as of January - ebooks.
Their selection isn't great, and they have some interface problems (use IE on a Windows PC; Firefox and Chrome have issues), but they do carry HarperCollins, Open Road, Scholastic, and some smaller publishers. A $3 HC novella cost me 9K points, there's a $1 short listed at 2500, a $10 indie novel-length anthology was 27K, and I've seen some new releases priced at over 40K.
There are certainly worse ways to get books than by absorbing points while watching the same TV shows I already follow.
Plus, my two "purchases" so far have been books that would've been problematic to buy from Kobo - the novella's an EPUB 3, and the anthology's publisher feeds PDFs to Kobo for reasons I cannot fathom. Watching the Grammys last night and The Flash tonight covered most of those points; I still have over 400K in my account.