Though similar in many ways, Reaktor is
much deeper, more complex and layered than Tassman. Note that this has both huge advantages and huge disadvantages, depending on your perspective.
It ranges from:
Loading pre-built ensembles at the highest level - which you can think of as "programs" that change it from a classic synth to a noise generator to a rhythm device to various types of FX processors to all kinds of other different things. Some of the ensembles that come with it, as well as other user's ensembles that can be downloaded from NI's site, are quite good and unique. Some, well, not so much. But they are tremendously varied and sometimes interesting regardless of how polished or quirky they are.
to
Patching pre-built building blocks like oscillator banks and filters to create synths (this level is probably most similar to Tassman).
to
Patching individual oscillators, filters, and all kinds of other stuff at a lower level.
to
Very low level DSP-type mathematical processing including trigonometry, exponents, logarithms, etc. down to the individual sample level.
IOW, it goes from a high "load a preset (ensemble)" level to a
very low level and pretty much everything in between.