OT: TTS Engine

Hi-

I'm sorry to bother you all, but I thought if anyone would know the answer,
the list would. I'm looking for a free TTS engine that works in as many
platforms/browsers as possible. I know that may be a lot to ask for, but if
anyone knows of a likely candidate, I would very much appreciate hearing
about it.

I would need it to have a promptable interface, so I can send it messages to
read, rather than simply having it screen-scrape. I am making an
accessibility example for SVG.

Regards-
-Doug

p.s. Please CC me privately, if you don't mind.