This library lets you write in the sky in Google Earth (and the Google Earth plugin) using KML LineStrings. It was developed as part of Pigeon Sim.
Here's a simple example usage.
A key part of the library is its homegrown, spindly font. I think I've included all the characters you're likely to see in everyday English, but very few accented characters are implemented. Pull requests welcome here.
A method returning a three.js THREE.Line might be handy.
This code is released under the GPL v3. To negotiate GPL-incompatible uses, feel free contact me.