Certain aspects of Apple's Mac OS X are "complete and utter crap" and "worse than Windows", according to Linux kernel creator Linus Torvalds.
Speaking to the Sydney Morning Herald, Torvalds also criticised Windows Vista and the GPL 3 licence, and said the marketing around OS releases such as Vista or Mac OS X Leopard is mostly about the visual shell around the OS, rather than the core functions themselves.
Furthermore, Torvalds believes all new operating systems are a waste of time and should "never have been something that people really care about... it should be completely invisible".
For Microsoft and Apple, big OS releases are mainly important as a way to force application and hardware upgrades, Torvalds said.
While OS X Leopard is "a much better system" than Windows Vista, Apple's OS has problems of its own, he said.
"OS X in some ways is actually worse than Windows to program for," he said. "[Apple's] file system is complete and utter crap, which is scary."
Torvalds has criticised OS X in the past, notably the Mach microkernel on which the OS is based. "Frankly, I think it's a piece of crap," Torvalds said of Mach in his 2001 autobiography, Just For Fun. "It contains all the design mistakes you can make and even manages to make up a few of its own."
Linux has yet to catch on as a major desktop OS, but Torvalds noted that this may change with mobile systems such as Asus' Linux-based Eee PC laptop.
Linux is well suited to mobile devices because it was originally designed for systems that, 15 years ago, had less computing power than the average mobile device today, Torvalds said. Dealing with mobile user interface issues has been a problem, but the Eee solves this by more closely resembling a standard PC.
The economics of Linux could encourage take-up by Asian hardware manufacturers, according to Torvalds.
"Software is really expensive to produce and takes years. If you're a hardware company you really can't afford that, you either have to be controlled from the outside, or take a pre-existing software stack that you can make changes to: namely open source," he said.
This could lead to a surge in Asian Linux-based machines. "I think that's one pretty exciting possibility, and it's where the market really wants to go," he said. "You can make a nice phone [or] video player, but if you want even fairly basic networking you need your own operating system."
Another significant front for Linux is green computing, Torvalds said. "We are now finally at the stage where, over the last couple of years, we have built all the infrastructure to be much better at power saving," he said.
He criticised the GPL 3 licence and, moreover, what he sees as the excessive attention such issues get.
"I think GPL version 3 is a bad licence, but it's not like it's the end of the world. Who cares?" Torvalds said.