F5 uses Tcl as the interpreter for iRules. Many people often ask why that is. This questions is usually followed up by an immediate, "Why not Perl?" or "Why not Java" or "Why not <fill in my preferre...
@richard, good to see that someone remembers that we used Tcl in the SnapGear routers. This was my doing. We used tinytcl, a modified version of Tcl 6.7 in order to fit into the small footprint of the low end routers. I'm still a big fan of Tcl and I maintain Jim Tcl (http://jim.tcl.tk/) which is a small-footprint implementation of Tcl designed for embedded systems.