"Here are some of the open source tools for text mining: information extraction, text classification, clustering, approximate string matching, language parsing and tagging, and more."
"Here is my short list of the most important open source [free] information retrieval libraries being used today that are undergoing active development as of writing."
This open source web-based calendar application is pretty good. Seems a bit clunky and I'm not sure about the scaleability, but there are few viable alternatives.