Retro AS-1 is a standard 3 oscillator analogue emulation. The main engine of AS-1 doesn't have a user interface - it comes with a control panel and editor to make changes. I don't like the way they have designed this. Upon installation it automatically installs its MIDI driver into Windows and when this MIDI driver is opened by any application the engine component is automatically loaded and automatically grabs the audio output of your computer.
So how about once it is installed and working? Well it has some nice features like state variable filters, both parallel and serial filtering (there are 2 filters per oscillator), the standard oscillator sync and FM modes. It has 2 effects processors per voice with delay, chorus, flanger, distortion, reverb and EQ available. The delay can be synchronised to MIDI. There is an arpeggiator (a feature which I have seen missing from a few recent programs) and a MIDI processor to enable layers and splits - most other soft synths require the use of external software to do this. Settings are spread over multiple tabbed screens - personally I prefer programs that squeeze as much as possible on one screen, but this is a matter of choice. It is 16-channel multi-timbral, but I would not want to run more than 1 or 2 sounds at once live from a single soft synth anyway. The sound produced is very good quality - it is capable of all the sorts of sounds you would expect from screaming leads to warm pads.
Retro AS-1 costs $260. Given the way the MIDI driver automatically loads the engine and the fact that there is nothing remarkable about this software this seems a bit much.