The Clie S360 shipped with the Palm 0S4.1 operating system installed. If your Clie has no operating system, you're prolly better off just getting a new PDA; I doubt you'll be able to find a stand-alone copy of 0S 4.1 (particularly as it was a 3Com product, and they sold off all their interest in Palm some time ago ) - mebbe on eBay, I dunno, didn't check. If your Clie does have an operating system, and what you're after is applications, CNET's Download.Com has a broad selection of
Palm OS - Compatible Software