Pro Tools HD – Digidesign’s 2002 hardware upgrade brought high resolution audio to the industry’s top DAW. Yes, this version truly made a difference in that there were a lot of questions regarding the sound quality of Pro Tools until HD came out. None now, it's the standard!
Apple Logic Pro – After the purchase of Steinberg, Apple puts its stamp on this popular music production tool making it a contender for top affordable native DAW. Don't know about Logic Pro as a game changer per se, but the fact that you can get great performance from a native (using only the host computer without the aid of additional processing cards) DAW certainly is.
Celemony Melodyne – The only competition for the ubiquitous Auto Tune app brought us a new way to correct pitch. The latest version of Melodyne is nothing short of amazing, providing some great forensic tools not usually associated with pitch correction.
JBL LSR6328P monitors – Once the studio monitoring champ, JBL made a solid bid for the title again with these great sounding speakers. Don't know how much of a game changer they are, but they're my choice and the ones I use every day.
Plugins – Many companies defined this category in the noughties including Waves, Sonnox, Focusrite, McDSP, Bomb Factory, TL Audio,SoundToys, PSP, URS, IK Multimedia, brainworx, Universal Audio,iZotope and more. Just as Pro Tools HD changed the way we thought about the sound of a DAW, the same can be said for the latest generation of plug-ins. No one even compares the sound to hardware anymore.
Now that the industry has made the conversion from hardware to software, more and more we see products that are evolutionary instead of revolutionary. I think a good case can be made for some of the above to be put in the revolutionary category. Wonder how many we'll see in the 10's?