Nuance 0.6.1
Unfortunately the author of the original project (Mike Perry) passed away a long time ago, but it seems like nobody picked up this piece of history and so there is no NUON emulator to be found anywhere except for his Nuance 0.5.1 release from 2007.
The source code of 0.5.0 (or is it actually 0.5.1??) was later-on released by his family via http://www.dragonshadow.com/-/downloads/NuanceExperimental.zip
By now, emulation was improved a lot with many games now working almost correctly (except for "random" endless loops that still occur in the emulated code due to whacky audio syncing) in the new 0.6.1 release.
Due to the (debatable) way how Mike designed the emulation core, this project is not trying to provide cycle-accurate emulation, but can rather be seen as a virtual NUON machine that provides as much computational power as possible from the host PC. The advantage: Games that stutter on original HW can run smooth. The disadvantage: Syncing problems (for now) in some games.