The Ciao Prolog system

Ciao is a modern Prolog implementation that builds up from a logic-based simple kernel designed to be portable, extensible, and modular. It features:

constraint logic programming and, in particular, Prolog, supporting the ISO-Prolog standard,
multiparadigm programming (meta-programming, higher-order, concurrency, functions, etc.)
user packages for syntactic and semantic language extensions, and interface with foreign code,
modules and bundles for large scale development, and assertions for unified static and dynamic verification.

Ciao can install natively in your operating system or run in the browser without installation.

%! \begin{miniplayground}
% Edit me!
% Code is loaded on the fly.
%
% Then type a query on the right,
%   ?- app(X,Y,[1,2,3]).

app([],Ys,Ys).
app([X|Xs],Ys,[X|Zs]) :-
     app(Xs,Ys,Zs).
%! \end{miniplayground}

The system implements some advanced features such as separate and incremental compilation, global program analysis and static debugging and optimization (via source to source program transformation, CiaoPP preprocessor), a build automation system, LPdoc documentation generator, debugger, and integrated development environment.