Poison-202 is described as 'is virtual synth that emulates the sounds of classic hardware synths from the '80s and '90s. The synth is capable of reproducing sounds from nearly any classic synth timbre'. There are eight alternatives to Poison-202 for a variety of platforms, including iPad, iPhone, Mac, AudioBus and Windows. The best alternative is Moog Model 15. It's not free, so if you're looking for a free alternative, you could try KORG Gadget. Other great apps like Poison-202 are DRC - Polyphonic Synthesizer (Paid), KORG iWAVESTATION (Paid), KORG iMS-20 (Paid) and Animoog (Paid).
DRC is a virtual analog synthesizer replicating the sound of hardware synths and featuring a minimal but powerful parameter set and cloud syncing for presets to make it easy to port patches to other devices.
Animoog captures the vast sonic vocabulary of Moog synthesizers and applies it to the modern touch surface paradigm, enabling you to quickly sculpt incredibly fluid and dynamic sounds that live, breathe, and evolve as you play them.