Joy-maker PopCap Games--developer of Peggle, Plants vs. Zombies and Bejeweled 3--has launched a new games label. 4th & Battery will make "experimental" games, including titles for "mature audiences."

4th & Battery's focus is on "small-scale, arcade-style games" for platforms including PC, iPhone and Facebook. The label expects to put out several games per year. That name, by the way, comes from the intersection where PopCap's Seattle headquarters is located.

"4th & Battery is a pressure valve intended to keep our heads from exploding," said PopCap executive VP of studios Ed Allard. "The PopCap brand has become closely associated with ultra-high quality, polish and attention to detail--which is a great thing. But our standard game development process is therefore long and involved, and doesn't really accommodate all of the creativity pumping through our collective veins. 4th & Battery gives us a way to quickly try really strange or marginal ideas, and to give our designers a safe area to hone their chops."

The first 4th & Battery game will be Unpleasant Horse, a free iPhone gaming starring, well, an unpleasant horse. The vile winged equine will fly through the skies, squishing birds and other horses for points and pushing them down into "a perpetual meat grinder." Not quite as sunny as your standard PopCap game, then.

Ever the pranksters, PopCap initially unveiled Unpleasant Horse on April 1, leaving a little confusion as to whether this was all one of those zany April Fools' Day hoaxes. Evidently, it's not.

Unpleasant Horse is due to launch for free later this month. Here's a teaser trailer: