[mattnewton]

If Google resources were used to create it (machines, the author's 20% time, google tools, etc), or if the author lives in a state/country without moonlighting protections.

I guess the former, and the author might be doing it as a 20% project owned by Google in the hopes of making it a larger, more successful project.

[kuschku]

That depends on jurisdiction, obviously.

If you do it during your break time, even if it’s produced on company machines, it remains yours, the company has no right to it. (in Germany).