Stuart Cassoff's "Communications Endpoints for Tcl" [L1 ] gives, among other functionality, UDP, IPv6, ...
["... significant demo of Tcl's extensibility (and Tcl_Channel's as well) ..."]
[... only internal mucking is through <tcl.h> ...]
[... fully compatible with socket, tls, ...]
[?Fit for folding back into core?]
"It has been designed so that Windows capability would be easy to integrate." As of May 2005, though, there's no Windows port.