Purpose: pointers to tutorials, books, tips, etc. for creating, interacting, etc. Tcl via the C API.
Tcl's original purpose, as detailed in John Ousterhout's seminal Usenet paper, [L1 ] [Anyone have a URL to this paper in html?] was to provide a developer with a standard language that could be embedded in their applications, providing continuity and ease learning curves. So in the beginning, the intent was that Tcl would be accessed only via the C API. Over the years, some have lost sight of that goal due to the simplicity of using the tclsh sample application that builds as a part of compiling the Tcl libraries.
[What are some Wiki pages that deal with this subject?]