One popular speech synth from back in the day, I believe it was WillowTalk, had a voice called Colossus, which sounded like the voice module of the computer from Colossus: The Forbin Project. This voice was used for that of CATS in the famous "All your base are belong to us" Flash video.
Another WillowTalk voice was a clone of DECtalk's Perfect Paul good enough to be used as the voice in the MC Hawking rap recordings.
It came from a company called Willow Pond Software. That seems to narrow searches down.
WillowTalk is apparently still of interest to Half-Life modders because another WillowTalk voice, possibly a clone of DECtalk's Huge Harry, was used as the Black Mesa VOX facility-wide announcement system in the original Half-Life.
Another WillowTalk voice was a clone of DECtalk's Perfect Paul good enough to be used as the voice in the MC Hawking rap recordings.