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 a tool to assist in the analysis of textual data. At the moment it only supports plain text formatted data.
R is a package that supports statistical data analysis, so if you want to combine thematic coding with case variable data, statistics and even some data mining tools, then RQDA may be a good choice.