Schismata's instrument designer allows you to build up each instrument by specifying the wave type and envelope shape for each harmonic.
Complicated sounds with varying harmonic content can be easily constructed with the graphical interface. Envelopes can be time dependant or note length dependant.
When you create a new instrument it appears in the "Band Room". When you have created a sound you like, you will be able to select it from the Band Room in any future compositions.
When you save your composition all the instruments you have used are saved with the file. So if you send it to a friend, they will have exactly the sound you wanted.

As you build your desired sound you can play it back and see the waveform in the "Viewer" window. Various techniques such as transforming one waveform into another, frequency modulation, dynamic control of waveshap parameters and phase, adding filters to individual components (harmonics) as well as globally allow you to quickly produce interesting instruments.