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 AudioUnit or VST plugins.
AudioUnit is Apple's audio plugin technology. These plugins provide sound effects that can be applied to the selected parts of your documents. A few AudioUnit effects are provided by Apple and are available on every Macintosh, such as a few filters, equalizer, pitch shifter, reverb and more.
Although Apple's AudioUnit effects can satisfy the most basic needs, many more AudioUnit plugins are made available by other companies. Some are free. Some very sophisticated AudioUnit plugins are available commercially.
VST (Virtual Studio Technology) is another plugin technology, created by Steinberg. Similarly to Audio Units, VST plugins can provide many effects for all kinds of audio work.
For virtually any sound processing work, there is an AudioUnit available. Compressors, expanders, sound cleaners that would remove noise or clicks...
You can browse the available plugins and make your pick from the lists available on these websites: