OpenSource, Text-To-Speech/SingingSynthesizer

Hatsune Miku is one of the best singing synthesizer. It is getting popular in the United States as well. (you type, Miku sings)

For opensource solution, Linux has several text-to-speech packages that work out-of-the box too. Do not overlook accessibility software, they can be amazing.
https://wiki.ubuntu.com/Accessibility/doc/LanguagesAndSpeechSynthesis

Say Hello World in your Linux terminal:
# espeak -v en "Hello World"