I'll just quote a post from Joss Whedon's blog and let it speak for itself:

So..... The bag is catless. During the strike I started writing a musical intended as a limited internet series, 3 episodes of approximately 10 minutes each. Writing with me was my brother Jed, his fiancee Maurissa, and my other brother Zack. To my shock and surprise, we finished it. To my greater shock and surprise, we managed (with the help of many people I'll be praising at length soon) to drag it into preproduction (yes, just as DOLLHOUSE was given a start date two months away and all my comics were due.) And today, after a grueling week of writing everything ever while trying to be a producer, I got to start shooting. A musical. This much I will say: It's the story of a low-rent super-villain, the hero who keeps beating him up, and the cute girl from the laundromat he's too shy to talk to. And I'm having the time of my life. "DOCTOR HORRIBLE'S SING-ALONG BLOG" Neil Patrick Harris.....as Dr. Horrible Nathan Fillion..........as Captain Hammer Felicia Day.............as Penny And a cast of Dozens! Coming soon.