There has been an effort underway within the Debian development community to pull the FreeBSD kernel within this distribution to provide an alternative to using the Linux kernel. In essence with this Debian GNU/kFreeBSD project you have the standard Debian package set providing a GNU user-land with a GNU C library, but the FreeBSD kernel is running underneath. More here

Of the 27 tests that were carried out with our first Debian GNU/kFreeBSD benchmarking session, in 18 of the tests Debian GNU/Linux 32-bit was faster than Debian GNU/kFreeBSD 32-bit. However, with many of those 18 wins, the GNU/kFreeBSD results were very close to the GNU/Linux numbers. With the 64-bit versions, Debian GNU/Linux did even better and was in front 23 of the 27 times compared to 64-bit Debian GNU/kFreeBSD. These 64-bit results were certainly quite interesting and it looks like the FreeBSD kernel can be better tuned for a 64-bit environment. Debian GNU/kFreeBSD 64-bit though did have strong advantages with the x264, 7-Zip, and Gcrypt CEMLLIA256-ECB Cipher tests over the Linux kernel