"JTcl" can mean one out of two things:

1. JTcl Interpreter, an implementation of Tcl (Tool Command Language) written in Java that implements a large extent of Tcl 8.4 syntax and commands, limited only by API restrictions of the Java Virtual Machine. It is based on the Jacl interpreter from the TclJava project.
2. The JTcl Java bindings for Tcl.