Glider is a Macintosh video game written by John Calhoun and first published as shareware in 1988 under the company name Soft Dorothy Software. The object of the game is to fly a paper plane through the rooms of a house. Air currents from heat ducts and fans affect the plane's movement, while assorted household objects are usually deadly. Some rooms have special mechanics, such as the ability to slide along grease-covered surfaces. Each room is presented as a two-dimensional side view. In 1991, a colorized version of Glider that included a level editor was published by Casady & Greene as Glider 4.0. A version of Glider 4 for Microsoft Windows was released around 1994. In 1994, Casady & Greene published a further enhanced version of the game, Glider PRO, for the Mac. When Casady & Greene went bankrupt in 2003, the rights to the series reverted to the author, who opted for a period of time to give the game away on his website. Calhoun wrote several other Macintosh games, such as Glypha, Pararena, and Stella Obscura, but Glider was the most popular. Gameplay The main challenge is to simply avoid collision with the floor, or obstacles such as furniture. Moving obstacles include bouncing basketballs, popping toast, and dripping water. Candles and other burning objects present both a handy updraft and a lethal flame. Collision with "enemy" paper planes and balloons is also fatal, but these can be shot down with the use of a bonus item: rubber bands. The other bonus items are pieces of paper (extra lives), a variety of clocks (points), and batteries (temporary increased speed.) Glider PRO includes two new bonus items: aluminum foil (shielding against in-flight collisions) and helium tanks (mutually exclusive with regard to batteries, allows the glider to float upwards). A puzzle element is added to the gameplay in the form of switches controlling vents, lighting, home applications and even enemies. Glider 4.0 was designed around rooms inside a house and the game's theme included such elements as claustrophobia and stormy weather. Glider PRO incorporated outdoor environments in addition to indoor environments, and had a different theme which included such things as sunny weather and the start of summer vacation. Houses Levels are called "houses" in Glider parlance, though a level may contain any number of individual buildings, as well as outdoors, sewer, or other sections. Houses are entirely self-contained, and any