Weft QDA is an easy-to-use, free and open-source tool for the analysis of textual data such as interview transcripts, fieldnotes and other documents. The software isn't being maintained or updated, but the current version is available and includes some standard CAQDAS features.
RDQA is a R package for Qualitative Data Analysis, a free (free as freedom) qualitative analysis software application (BSD license). It works on Windows, Linux/FreeBSD and (probably) the Mac OSX platforms. RQDA is an easy to use tool to assist in the analysis of textual data.
CAT is a free service of the Qualitative Data Analysis Program (QDAP), and hosted by the University Center for Social and Urban Research, at the University of Pittsburgh, and QDAP-UMass, in the College of Social and Behavioral Sciences, at the University of Massachusetts Amherst. CAT was the 2008 winner of the "Best Research Software" award from the organized section on Information Technology & Politics in the American Political Science Association.