The Aurora Compressor/Sustainer is an updated version of the MXR Dyna Comp and the Ross Compressor. One of the first compressor circuits designed for guitar, the MXR Dyna Comp has been a consistent favorite among guitarists, and the circuit is legendary in the DIY community.
The Ross Compressor was an updated clone of the Dyna Comp that got a lot of attention when it was “rediscovered” in the 1990s by Trey Anastasio of Phish. It has better power supply filtering and thus lower noise, but is otherwise very similar to the Dyna Comp.
The Aurora takes things a step further by adding a couple of modifications. First, the obsolete CA3080 has been replaced by the LM13700, which is essentially just a dual CA3080 but with the advantage of still being in production and easy to find.
The output section has also been modified to take the signal from a different part of the envelope detector. This results in drastically reduced ripple (which is perceived as distortion on the otherwise clean signal). Some people like this distortion, so the Aurora was designed so you can still build the “stock” version and use the classic output stage. See the build notes for more details.