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)
Honorable mention... Check out Adam Szabo's Viper, a recreation of the infamous Access Virus synth.
An example of what Flowstone is capable of taken to the extreme: Viper introduction