Installing ported Posix applications is an easy process, you simply untar them to your /usr/ and then run the pkmanager -a /usr/* command to update the enviroment settings that these apps may require. Currently, there are around 210 applications available for AtheOS, but only about 35 of them are GUI-based. Of course, the flagship GUI application for AtheOS is ABrowse (included in the base installation), a very capable web browser, based on the KDE Konqueror's KHTML KPart. It is funny to see ABrowse loading in 1 second on my K6 300 Mhz laptop's extremely slow hard drive, while Konqueror takes 5-6 seconds to start-up on my dual Celeron 533 with 256 MB of RAM and the speedy IBM 30 GB IDE hard drive (yes, my whole KDE install is object-prelinked).
AtheOS, like with BeOS, loads all its drivers when it boots and then selects which one is supported and which one is not. There is no IDE driver so far, which is why AtheOS does not support reading from a CD-ROM or 'talk' to the hard drive directly. It uses the BIOS for reading and writting the hard drive and the floppy drive. I noticed on my AMD K6-2 300 Mhz laptop that each time AtheOS touches the floppy, the mouse cursor does jerky movements and becomes a bit unresponsive. While it behaves better than the Win9x/ME codebase on the specific floppy/mouse issue, it is still away from delivering a comfortable experience. Maybe the fact that you have to go through the BIOS has to do with this though (BIOS is 16-bit while AtheOS is 32-bit and it has to momentarily switch to 16-bit mode in order to 'talk' to the BIOS).
Not much hardware is supported on AtheOS, but it is enough to allow most of the PC configurations today to work flawlessly (you will need a FAT16/32 partition though to complete the installation - except if you are cool to mess up with 12+ floppy disks). There is an SBPro sound driver, 4 graphics drivers including nVidia chipsets (unsupported gfx chipsets will have to use a painfully super-slow VESA), all IDE hard drives and the SCSI ones that expose themselves to the BIOS are working, and 3 network card chipsets. PPP and modems are not supported and probably they never will, according to Kurt. 32 MB of RAM is more than enough for the OS itself, however if you are planning to do any kind of development, you will need at least 128 MB, as AtheOS VM and kernel scheduler can choke easily (eating up all your system's resources with only resort to reset the PC) on anything less than 128 MB RAM in some 'heavy' GCC compilations. AtheOS' swap support is disabled for now (there is one, but it does not work after it got broke after an AtheOS release 2 years ago).