On Linux, you'll want something that uses AT-SPI, which most modern Linux GUI applications support. Orca seems to be the common one for GNOME, at least: http://en.wikipedia.org/wiki/Orca_%28assistive_technology%29 I haven't tried Orca so I can't say how well it works. Unfortunately, Wine does not currently bridge any Assistive Technology APIs in either direction. That means Windows applications running in Wine will not work with Orca, and native Linux applications will not work with a Windows screen reader. I'm not aware of any technical reason why we couldn't do this, there just hasn't been a demand or drive for it.
