There is one in Anarki: http://github.com/nex3/arc/tree/master/help/

Usage examples:

  arc> help.acons
  [fn]  (acons x)
   Determines if `x' is a `cons' cell or list.
      Unlike 'alist, this function will return nil if given an empty list
      See also [[atom]] [[alist]] [[dotted]] [[isa]] [[cons]] [[list]] 
  nil
  arc> help.alist
  [fn]  (alist x)
   Return true if argument is a possibly empty list
      Unlike 'acons, this function returns t when given an empty list
      See also [[atom]] [[acons]] [[dotted]] [[isa]] [[cons]] [[list]] 
  nil
  arc> help.afn
  [mac] (afn parms . body)
   Creates a function which calls itself with the name `self'.
      See also [[fn]] [[rfn]] [[aif]] [[awhen]] [[aand]] 
  nil