"I wanted to have a system whose templates looked like HTML, with a minimum number of extra tags. . . . Web Templating owes a lot to the Ars Digita Community System (ACS) ..." [L1 ]
AMG: I highly recommend JCW's [substify], found near the top of Templates and subst. I use a variant of it to drive my Web site [L2 ], including a custom search engine I made for a friend. See my code here: [L3 ]. First look at template [L4 ], then look at [emit_template] in site.tcl [L5 ], which is called near the bottom of script [L6 ].
FF: look at TemplaTcl: a Tcl template engine, maybe is the one you are searching for. It has just two tags, ASP-like, and it is easily expandable, and relatively safe, as it runs in a safe interpreter.