replxx is described as '- A readline and libedit replacement that supports UTF-8, syntax highlighting, hints and Windows and is BSD licensed'. There are three alternatives to replxx for Linux, Mac and BSD. The best alternative is GNU readline, which is both free and Open Source. Other great apps like replxx are libedit (Free, Open Source) and Linenoise (Free, Open Source).
This is an autotool- and libtoolized port of the NetBSD Editline library (libedit). This Berkeley-style licensed command line editor library provides generic line editing, history, and tokenization functions, similar to those found in GNU Readline.