Quirky Linux (http://bkhome.org/blog/?viewCat=Quirky) and Debian Lenny based Puppy dpup (http://www.dpup.org) seem to be actively developed and based on the Puppy Linux philosophy. Both are based on Woof but are based on T2 and Debian Lenny respectively. There are other Woof Puppy based on Slackware and Ubuntu but none of them seems to be as mature as Quirky and dpup.
I tried Quirky 0.02 and now I am running Quirky 0.03. One of the issue is that the default selected Xorg nv driver is not working for my Nvidia 620i/Geforce 7050 integrated graphics and I have to use Xorg vesa driver. Moreover, I am not able to install the Nvidia proprietary driver as it complains that it is not able to load the kernel driver. But it is not too bad, I am still able to reach full resolution of 1280x1024 (16bpp now) on my LG L1750SQ LCD monitor whereas distros like Ubuntu can not reach this resolution without using the Nvidia proprietary driver. It is also quite fast. I feel it is faster than Puppy 4.3.1.
From what I see, dpup is less matured even though it is supposed to be one of the leading V5.x Puppy. I feel it is slower than Quirky.