System partially frozen: cannot alt-tab or force-quit, but can login over AFP... how to fix without hard reboot?

So I was using Safari on my Mac Pro and randomly, for the first time ever, the system became unresponsive, except I can still move the mouse cursor (which is stuck as an I-beam), and I can login to the machine over AFP, browse its drives, etc.

I prefer not to hard reboot my computer. But I cannot alt-tab out of Safari, I cannot force-quit Safari, and I cannot click on any menus or use the Dock. Which is odd because I can still move the mouse cursor.

This is a really weird type of freeze I've never seen before. This machine has been working flawlessly for five years.

Since I was able to login over AFP, is there anything that I can do to resolve this without hard-rebooting the Mac Pro?

Note: I unplugged all USB, DVI, and FW devices (except my TimeMachine drive) and plugged them back in, to no avail.