Korektor started with Michal Richter's diploma thesis Advanced Czech Spellchecker, but it is being developed further. There are two versions: a command line utility (tested on Linux, Windows and OS X) and a REST service with publicly available API and HTML front end.
The original OS X SpellServer providing System Service integrating Korektor with native OS X GUI applications is no longer developed, but do not hesitate to contact us if you are interested in it.
Copyright 2015 by Institute of Formal and Applied Linguistics, Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic.
Korektor website http://ufal.mff.cuni.cz/korektor contains download links of both the released packages and spellchecker models, and hosts documentation.
Korektor repository http://github.com/ufal/korektor is hosted on GitHub.