Critter is a cross-platform

Cross-platform

In computing, cross-platform, or multi-platform, is an attribute conferred to computer software or computing methods and concepts that are implemented and inter-operate on multiple computer platforms...

 chess engine by Slovakia

Slovakia

The Slovak Republic is a landlocked state in Central Europe. It has a population of over five million and an area of about . Slovakia is bordered by the Czech Republic and Austria to the west, Poland to the north, Ukraine to the east and Hungary to the south...

n programmer Richard Vida which is free for non-commercial use in UCI

Universal Chess Interface

The Universal Chess Interface is an open communication protocol that enables a chess program's engine to communicate with its user interface....

 format. The engine has achieved top five of most official chess engine ELO rating

Elo rating system

The Elo rating system is a method for calculating the relative skill levels of players in two-player games such as chess. It is named after its creator Arpad Elo, a Hungarian-born American physics professor....

 lists, generally bested primarily only by Houdini

Houdini (chess)

Houdini is a chess engine for Windows, by Belgian programmer Robert Houdart. Free for non-commercial use , later versions are not free. Since the release of version 1.5 on 15 December 2010, it has taken the top spot in every rating list that includes it...

 and Rybka

Rybka

Rybka is a computer chess engine designed by International Master Vasik Rajlich. , Rybka is one of the top-rated engines on chess engine rating lists and has won many computer chess tournaments...

. The first version was originally written in Delphi

Object Pascal

Object Pascal refers to a branch of object-oriented derivatives of Pascal, mostly known as the primary programming language of Embarcadero Delphi.-Early history at Apple:...

 but the code was converted to C++

C++

C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...

 using Bitboard

Bitboard

A bitboard is a data structure commonly used in computer systems that play board games.A bitboard, often used for boardgames such as chess, checkers and othello, is a specialization of the bitset data structure, where each bit represents a game position or state, designed for optimization of speed...

technology because Delphi did not perform well under 64-bit processors.