Open 2sky is a full-featured planetarium application for Palm OS, released as open source by Kevin S. Polk in 2010.
Some of its features include:
Star catalogs up to magnitude 11 (and smaller catalogs for devices with limited memory).
NGC, IC, and Messier catalogs.
Solar System objects, including the Sun, Moon, planets, Pluto, bright moons of Jupiter, major asteroids, bright comets and meteor shower radiants.
Ability to manually import new comets and asteroids from Memo.