HelenOS 0.5.0 represents improvements made to this open-source operating system since March of 2011. Some of the key improvements to this original operating system are USB support (USB v1.1). a re-implemented networking stack with full TCP support, Realtek RTL8139 / Intel E1000 network drivers, read-only EXT2 and ISO9660 file-system support, read-write MINIX FS support, and some new ported applications. The ported applications to HelenOS include GNU Binutils, PCC (Portable C Compiler), and MSIM (MIPS R4000 simulator).
Some other highlights of HelenOS 0.5.0 include uni-processor support for IA64, reviving the PowerPC 32-bit support, memory servation support in the kernel, a new Serial ATA driver for QEMU, FAT file-system improvements, and GRUB2 is being used for booting IA32 and AMD64 kernels.
More details on HelenOS 0.5.0 can be found from the announcement page and release notes. HelenOS 0.5.0 is freely available here for AMD64, ARM32, IA32, IA64, MIPS32, PowerPC32, and SPARC64 architectures.