The extensive line of Acqua plugins are based on Nebula tech, both developed by Acustica. An advanced type of convolution is involved to replicate the sound of hardware devices, with varying levels of success (IMHO), but the more recent offerings are certainly worth checking out.
Improvements to the underlying engine ("core") have been coming out frequently, the main benefit of which has been compressor models. Until recently, Nebula compressor libraries have not been known for accurate compression action, perhaps due to limitations in how quickly the engine could adapt to input levels. The newer models effectively mitigate that drawback, at the cost of generally high CPU usage.
As always, Nebula excels at steady-state hardware simulations such as EQ and tape saturation. When it comes to those, there aren't many traditional algorithmic plugins that can match the sound available from the best Nebula-based products. Now that compression has been brought up to speed, these are fast becoming the plugins to beat in many cases.
Nebula has been around for years, but was never exactly user-friendly. The Acquas are much easier to deal with, acting just like a normal VST plugin. Still, Acustica lags its competitors in providing a smooth user experience for demos, installation, authorization, support, etc. The demo procedure is particularly complicated, but if you're patient enough you'll be rewarded with a whole new world of plugin tech to explore. It's worth the effort.
Cheers,
Eddie