TEXOR (Topic Extractor) has been specially designed to process chats. The main problem with them is abundance of non-standard lexicon and spelling errors. We developed a module for spelling correction and algorithms for detection of chat topics.
TEXOR provides as output topics of chats expressed in key-words concentrating on the terms that denote undesirable events, such as acts of violence or terrorism.
You can try online version of Texor at http://www.cll.khsu.ru/chatsumm/main.aspx