It doesn't look like it's available from the developer/Apple.
My most recent local copy is version 4.92 which dates to 2010-01-14. This works fine on my 2008 MacPro (desktop tower) but may not work properly for newer hardware.
You could look into XRG if you need a free system/hardware monitor. The only noteworthy difference is that XRG lacks a fan RPM listing but instead has a GPU memory usage graph.
This is the website:
http://www.gauchosoft.com/Products/XRG/
Nice! It has temperature monitors, too, which is always a good thing. I'm just lucky this computer hasn't had a fan issue like my last two.
But it doesn't break down how much wired memory each process is using; it just shows the total wired memory in use, which is the same information I get from Activity Monitor.
I mostly use XRG and the iStat Pro Dashboard widget (this precedes the more recent iStat Menus app) - both of these are free.
XRG shows CPU usage, RAM usage, Temperatures, Network activity and Disk activity. It can also be styled in various ways.
In Linux there is Conky a text config file you modify to add different features, I'm not sure what the OS X equivalent is.
Here's a post at Ars forums discussing alternatives.
People seem to agree XRG is the best way.