Tcl has a distinguished record of accomplishment in supporting [architecture]s 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. (GWL - That piece of CPU was sold to AspenTech in the early 2000s. AspenTech the buried everything they bought from CPU.)Apparently XMLblaster  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.
The "msg"  interface that is used to operate F5 instrumentation at the MMT Observatory . This client/server API includes a complete pub/sub synchronous or async passing of scalar values and RPC of procs. It's designed to be "so easy" that even a PhD can use it. The code is here. JBR
A paper presented at the 11th Annual Tcl/Tk Conference  explains how Tcl/Tk was interfaced to the Information Sharing Protocol (ISP) used in the Mission Control Center (MCC) at the Johnson Space Center (JSC). The interface provides an easy publish, subscribe, and filter interface for Tcl/Tk applications.
[Explain how Tequila can be regarded as publish-subscribe.]
[Do CORBAites use EventService to build publish-subscribe infrastructure?]
Also the STOMP implementations should fit in nicely here.