If you are exploring creative audio design, we recommend trying the official MetaSynth demo. If you'd like, I can: Explain how to use the room in detail. Suggest free alternative software for spectral synthesis. Tell you more about U&I Software's other products.
If you are determined to have the original MetaSynth experience, the safest and most ethical path is to purchase a legitimate license directly from the developer. While it is a discontinued product, licenses are still available for purchase from the official U&I Software website, sometimes with discounts available for students, teachers, or via promotional offers. You can also find legitimate second-hand license transfers from users on forums like those for Ableton or KVR Audio.
Metasynth 5.3 is a versatile software that can be used in various applications, including: