Another effort along the same lines is "Tcl Direct Interface" which I wrote. I was inspired by dllcaller but had some different ideas on how it should be done. Some of my ideas got back to dllcaller. But both dllcaller and "Tcl Direct Interface" could not claim the support and the numerios platforms that ffidl has.
You can still get "Tcl Direct Interface" from http://sourceforge.net/projects/tcl-dll-caller but no active development has been done in a while. Robin Beckers site seems to be gone.
(Sept-1-2003)Robin's site is here: http://www.jessikat.fsnet.co.uk/index.html
(Dec-12-2015)and now here: http://www.jessikat.plus.com/index.html