+* Racket [FFI](http://docs.racket-lang.org/foreign/index.html) |
+[C API](http://docs.racket-lang.org/inside/index.html)
+* [Unsafe operations](http://docs.racket-lang.org/reference/unsafe.html)
+* [Initialization etc](http://docs.racket-lang.org/reference/running-sa.html)
+
+## Teaching Languages ##
+
+* [DrRacket/How to Design Programs Teaching Languages](http://docs.racket-lang.org/drracket/htdp-langs.html)
+* [HtDP Languages](http://docs.racket-lang.org/htdp-langs/index.html)
+* [HtDP Teachpacks](http://docs.racket-lang.org/teachpack/index.html)
+* [Implementing HtDP & other customized teaching languages](http://docs.racket-lang.org/htdp/index.html)
+
+## Custom Languages ##
+
+Racket users can define their own languages, as discussed in [Creating Languages](http://docs.racket-lang.org/guide/languages.html). Typically, a language name maps to its implementation through a module path by adding `/lang/reader`; for example, the language name `scribble/base` is expanded to `scribble/base/lang/reader`, which is the module that implements the surface-syntax parser.
+
+* [Syntax: Meta-Programming Helpers](http://docs.racket-lang.org/syntax/index.html)
+* [(require syntax/module-reader)](http://docs.racket-lang.org/syntax/reader-helpers.html#%28mod-path._syntax%2Fmodule-reader%29)
+* [#lang racket/kernel](http://docs.racket-lang.org/reference/Kernel_Forms_and_Functions.html)
+
+* [Extending DrRacket/Teachpacks](http://docs.racket-lang.org/drracket/extending-drracket.html#%28part._teachpacks%29)
+* [Adding Languages to DrRacket](http://docs.racket-lang.org/tools/adding-languages.html)
+* [#lang](http://docs.racket-lang.org/drracket/module.html) [more](http://docs.racket-lang.org/guide/Module_Syntax.html#%28part._hash-lang%29)
+* [Output Printing Styles](http://docs.racket-lang.org/drracket/output-syntax.html)