This folder contains everything related to 3rdparty code or tools.

cmake - scripts for the cmake build system (http://www.cmake.org)
libconfig - library for processing structured configuration files (http://www.hyperrealm.com/libconfig/)
mysql - library for MySQL Community Server (http://www.mysql.com)
pcre - library for Perl Compatible Regular Expressions (http://www.pcre.org)
zlib - library for DEFLATE lossless compression algorithm (http://www.zlib.net)