I took it to mean "sandbox"
It's not as common as some would have you believe but it is real. A teammate spent his 20% on underwater topography on Google Earth and another spent his on the glider thing.
Having an employee turn up a popular side projects while being vendor-locked onto your platform sounds like it should be more popular among rich people.
The way it is should actually be sold to the average entry-level fresh-out-of-college Google hire is probably closer to the way I framed it, though, than the examples of Gmail and Google Calendar which are pretty much two unicorns.