Automatically remove DC Offset
Manually add DC Offset
The ability to add DC Offset enables users to apply some effects (e.g. hard limiting) to mostly/only the positive or negative side of the waveform, then return the waveform back to center.
There are quite a few “unofficial” plug-in in this section of the forum: http://forum.audacityteam.org/viewforum.php?f=42
Many of them are “experimental” or not widely tested.
User feedback about plug-ins in that section of the forum is very helpful in deciding if a plug-in is “ready” for putting on the wiki.
Feel free to browse that forum board, and comment on any plug-ins that you try.