If you want very robotic synthy sounds, the best option is probably Chipspeech, because that emulates various vocal synths from the 1960s to the 1980s in a seriously researched and accurate way. There are also sample libraries with wordbuilders, like Realivox Blue and various choral libraries. UTAU is also popular and free and has a ton of voices available, but it's a pain to deal with for languages other than Japanese. While I'd like to find the exact same application for old time's sake, I'll happily take recommendations for other ones that do the same thing. Sbaitso, or if you know your Aphex Twin, the creepy voice at the end of Funny Little Man ('I would like to f**k you up the bumhole and then I will sneak in to your room.'. The results were funny as hell and I really want to find it! The voice synth sounded something like Dr. You needed to use codes: I think 'phone arpa on' was one of them, to turn the singing effect on, then you would use values like '120,60' to choose pitch and note length and type phonetic 'sh'/'ch'/'ah' sounds to make it sing songs, all in a basic Notepad-esque way. You could type in text and it would say it back in a choice of voices, but crucially, it would sing too! I think it was software bundled with SoundBlaster AWE32 or AWE64. The software I'm talking about existed over 15 years ago but I can't find anything like it now.

Text to speech singing