The team from ReactOS is getting close to the magic 0.4 release.
They've solved a lot of problems and two key areas which stand out are the much improved network stack and the emergence of sound support in the kernel via the new kernel streaming services.

Announcement | Changelog | Download

From the changelog:

• Reduced minimum memory requirement to 32Mb. In theory ReactOS can now be installed with 24Mb and run with only 20Mb
• A new, faster Hyperspace Mapping Interface has been implemented in the kernel resulting in a speed improvement of over 300%
• Security check improvements to the Object Manager in the kernel improves performance by 500%. Noticeable during large file/registry operations
• Various NDIS and AFD problems have been solved which increase compatibility with 3rd party NIC drivers and hardening of the network stack
• Preliminary support for sound via the new Kernel Streaming service. It's now possible to use the ac97 driver via our new Port Class library to play sound bytes using winamp
• A great deal of work has been put into the command prompt to make it much more compatible. It's now able to run very complex scripts, including our own Build Environment
• Many bugfixes to the kernel mode portion of the GDI resulting in much improved drawing engine across all bit depths
• Synchronization of most of the Wine usermode DLLs