Here you'll find technically much more advanced plugins than Saguaro.one. Rex at Flowstoners.com has created a ton of VST plugins using FlowStone. Ranging from synthesizers, samplers and effects to various simulations of rare acoustic instruments. Alot of his creations are based on physical modelling techniques.
Take a listen to Rex and his plugins (youtube) and try some of them out. His Flowstoners page also feature other creators plugins as well...
A pipe organ simulator. One of many examples of Rex's plugins and a further development of his first Rank plugin...
Quilcom SIM-HG
Instrument:
Simulates different types of Hurdy Gurdies using a wide range of parameters
Quilcom SIM-MBIRA
Instrument:
Simulates an African Mbira (knows as Kalimba in the westernised version)
http://kbrownsynthplugins.weebly.com/
K Brown has built a myriad of different synths and equalizers. Well over 100 of them.
Not emulations, but structurally based of original hardware synths. Some with added/enhanced features beyond the original....
Also check out Adam Szabo's Viper, a plugin recreating the sound and aspects of the infamous Access Virus synth. Psytrance instrument number 1.
Viper is a commercial project that shows what Flowstone's engine is capable of in the hands of a pro developer, with help from the best and possibly the creator of FlowStone itself.
Professional in every single detail...