A PlayStation Portable remake was released as Ape Escape: On the Loose in North America, Saru Get You P! (サルゲッチュP!) in Japan and Ape Escape P in Europe. It was developed by SIMS and published by Sony Computer Entertainment. It was released on March 17, 2005 in Japan, March 22, 2005 in North America and May 5, 2006 in Europe. It features 2-player minigames that can be wirelessly played between 2 PSP systems. In North America, it was one of the system's launch titles and is one of the first titles for the PSP Greatest Hits collection.
One key difference between On the Loose and the original Ape Escape (apart from the new aspect ratio, 16:9) is that this game can only be played with one analog stick. Also, the R shoulder jump button was replaced with the crawl action, and the jump button is now the x button, meaning the amount of Gadgets the player was allowed to have at once was reduced from 4 to 3. The first unlockable minigame was also changed. The PS1 version was Rocket-ski racing, and you used both analog sticks to control the appropriate ski. In the PSP version, since there is no second analog stick, the skis were changed to snowboards. The tracks were also changed to a Slalom over the original Circle circuit. For an unknown reason, the stage "Wabi Sabi Wall" was renamed to "Tiki Tiki Wall".
Source: Wikipedia, "Ape Escape (video game)", available under the CC-BY-SA License.