Apart from a few relatively simple effects, such as fades in/out, silences or the reverse effect, most of TwistedWave's effects are available throught Audio Unit or VST plugins.
Audio Units is Apple's audio plugin technology. These plugins provide sound effects that can be applied to the selected parts of your documents. A few Audio Units are provided by Apple and are available on every Macintosh, such as a few filters, equalizer, pitch shifter, reverb and more.
Although Apple's Audio Units can satisfy the most basic needs, many more Audio Units are made available by other companies. Some are free. Some very sophisticated Audio Unit plugins are available commercially.
For virtually any sound processing work, there is an Audio Unit available. Compressors, expanders, sound cleaners that would remove noise or clicks... A comprehensive list is available on macmusic.org.
VST (Virtual Studio Technology) is another plugin technology, created by Steinberg. Similarly to Audio Units, VST plugins can provide many effects, and a comprehensive list is also available on macmusic.org.