From the Phoronix perspective, here's the ten best features of FreeBSD 10.0 (listed in no particular order):
1. AMD Radeon KMS support has finally made it to the BSD world. Recent Linux kernel code from the open-source AMD DRM/KMS graphics driver has been ported to FreeBSD along with updated user-space Mesa and xf86-video-ati code. This will allow for accelerated rendering on more hardware, better performance, and for some GPUs it finally means being able to display the right resolution on your BSD system. It's a big step forward after Intel KMS landed in FreeBSD 9 but still using the NVIDIA binary driver is likely the best bet for FreeBSD desktop users.
2. The Bhyve hypervisor has been merged for providing new virtualization support for FreeBSD servers. Still though it will likely be some time before Byhve can truly compete with Xen and Linux KVM.
3. The popular low-cost Raspberry Pi ARM development board finally works on FreeBSD. There's also other ARM FreeBSD architecture improvements in this next release.
4. ZFS file-system improvements. FreeBSD and other BSD distributions continue advancing with their open-source ZFS file-system support. In FreeBSD 10.0 there is now ZFS TRIM support for solid-state drives, write optimizations, LZ4 compression support, L2ARC compression support, and various other file-system optimizations. Some of these ZFS improvements were ported from the Illumos code-base.
5. USB audio support has improved significantly with new hardware support, bandwidth optimizations, increased sampling frequency, and other changes.
6. LLVM Clang is the default C/C++ compiler in the FreeBSD base system now in place of GCC. The GNU Compiler Collection will continue to be available via FreeBSD Ports, but LLVM/Clang is the preferred compiler for its more liberal licensing, fast build times with lower memory use, and other reasons.
7. Complementing the Byhve support in FreeBSD 10.0 is also support for Microsoft's Hyper-V hypervisor. This FreeBSD support for running as a guest on Microsoft's virtualization platform was done by Microsoft along with NetApp and Citrix. Microsoft has long been contributing to the Linux kernel for their virtual drivers and now they're committing to FreeBSD too.
8. Intel AES-NI instruction support for speeding up some encryption/decryption tasks. FreeBSD 10.0 also supports Intel's RDRAND "Bull Mountain" hardware random number generator. FreeBSD isn't making exclusive reliance on these hardware random number generators though given the recent NSA / Snowden allegations.
9. Improved 802.11n WiFi networking suport. There's improvements to the kernel's net80211 stack, support for up to three stream 802.11n configurations, and new hardware support. Atheros hardware is one of the big winners with these wireless networking improvements. On a similar note, 802.11s mesh support was added as well.
10. FUSE is now part of the FreeBSD base system for better promoting File-Systems in User-Space. This will better the NTFS support on FreeBSD as one of the notable FUSE-based drivers, but there's also a growing number of FUSE file-systems. Previously FUSE was just available in ports.
Many more details on the FreeBSD 10.0 changes can be found via the FreeBSD Wiki. Stay tuned to Phoronix for the official FreeBSD 10.0 announcement in the days ahead.