Sling started as an internal project at Day Software , and entered the Apache Incubator in September 2007. As of June, 17th, 2009 Apache Sling is a top level project of the Apache Software Foundation.
The name "Sling" has been proposed by Roy Fielding who explained it like this:
[The name is] Biblical in nature. The story of David: the weapon he uses to slay the giant Goliath is a sling. Hence, our David's [David Nuescheler, CTO of Day Software] favorite weapon.
It is also the simplest device for delivering content very fast.