tomixornot
1. Is the Tassman 4 (AAS) some how similar to Reaktor ?
2. What are the Reaktor Prism / Spark ? How are they related to Reaktor (since they share the Reaktor name) ?
3. Some other products are listed as related to the Reaktor such as Razor, The Mouth, The Finger.. Are they completely different products or similar to Reaktor Prism / Spark (if these are related to Reaktor).
I consider T4 and Reaktor to be similar yes - Tass is a physical modeling synth primarily, but that description limits it. While Reaktor has physical modeling capability it also has a great deal more. Both are modular synths with the capability to create a whole host of synths, effects, sequencers, etc, if you've got the time to commit to them. Both also have a large user library, (Reaktor's is much richer and more diverse) and a developed/developing library of optional, extra cost synths developed in the core environment - For AAS it's chromaphone, String Studio, etc, for Reaktor, it's Spark, Razor, the Mouth, the Finger, etc.
I own both and while there are a lot of similarities as noted above, I think they are unique in their own way. Both are really excellent.
If you own Tass 4 already I don't think you'd buy Reaktor at $99 and wish you hadn't due to the similarities.