Tcl has a distinguished record of accomplishment in supporting architectures based on the publish-subscribe pattern. One prominent domain is process control, where CPU bound Tcl to Tibco and MQ middleware, as well as a home-grown publish-subscribe bus. CPU's current owners apparently have "buried" all these products.
Apparently XMLblaster [L1 ] still lacks a demonstration client in Tcl as 2004 begins, although someone (? Benno Lange?) was working on it. It ought to be straightforward ...
Tuplespace is a publish-subscribe mechanism, one with at least a couple of distinct advantages, including the ease with which one can register interest in a pattern, and not just a variable.
[Explain how Tequila can be regarded as publish-subscribe.]