incr Tcl (commonly stylised as [incr Tcl], and often abbreviated to itcl) is a set of object-oriented extensions for the Tcl programming language. It is widely used among the Tcl community, and is generally regarded as industrial strength. Its name is a pun on "C++". Itcl implementations exist as both a package that may be dynamically loaded by a Tcl application, as well as an independent standalone language with its own interpreter.