This is what synthetic singing sounded like back in the 90's:
Apoptygma Berzerk - Kathy's Song (Skip to 2:55 if you want to miss a good song.)
My intro to this subject was Kelly's MacinSinger. It's amazingly still available for download, but you need Hypercard and Mac OS 7-9. If you at least have the latter in some form and an old copy of Netscape, you could also try this.
You may think making a VSQX seems pretty laborious, but that's peanuts to MacinTalk 3. The only input method was to write pitch, tempo and phoneme instructions manually into a text editor, then you'd highlight the text and pick one of a few halfway passable voices. It was totally the coolest thing EVER. At least good for 15 minutes of fun or so.
Pretty amazing how far we've come since then.
EDIT: Since HAL 9000 was brought up - here, have a bonus huge box from the 60's singing a lovely little tune.