Deadmau5

Deadmau5 on FL Studio:

"First and foremost, I launch FL with the beginning of each little idea I have in my head, whether it’s a fast melody, or a drum groove to start out with. I Use FL Studio for that because I have found that the piano roll is by far the FASTEST way to “plot” my melodies and rhythms down because although I have an ear for it, I couldn’t “play” a melody to save my life. So the base of the track is composed almost entirely in FL Studio, all my piano roll / midi data is stored in FL Studio."

Starting at 3:22 in the video, Joel states "Aw, I mean at the end of the day, you're gonna be digital. I mean, this shit is all going into Ableton, or Cubase, or Pro Tools, or fucking whatever I'm using at the time. It's all gonna get there one way or another, which is digital..."

In a Tweet, Deadmau5 makes reference to Pro Tools version 9: https://twitter.com/deadmau5/status/549459947683840

More proof from http://lat.ms/1dZe7cm "The Nine Inch Nails fan got his start hanging out in Niagara Falls studios and record stores. He became a Pro Tools expert and began making his own tracks. In the information diaspora of the Internet age, those tracks found some powerful friendly ears. Fellow Pro Tools guru Steve Duda passed one to Mötley Crüe drummer Tommy Lee. Zimmerman, who was still living with his mom at the time, and Lee bonded over beats and became close friends and collaborators."

In this footage from one of Deadmau5's Livestreams, he uses Ableton Live extensively. The logo on the highlighted (currently-open) window is a gray square— the square logo is exclusive to version 9 of Ableton, and the gray is indicative of the Suite edition. As such, it's safe to assume that the version of Live 9 he's using here is the Suite edition.

In this video stream the item is seen all over the screen whereas on the top left corner is where it says "REAPER v5.40/x64".

Deadmau5 is using Bitwig Studio in his April 08, 2014 Live Stream. The opening shot of the video recording of his stream is the interface for Bitwig Studio itself, and the logo can be spotted in the upper-left corner.

At 20:40 in this video, deadmau5 mentions how he prefers to resample in Audacity.