Weft QDA is a free open-source easy-to-use software tool for the analysis of textual data such as interview transcripts, field notes and other documents.
Weft QDA is no longer being updated and there are now free (but not open source) versions of some commercial software such as QDA Miner Lite
You may find this program useful because of its simplicity. It was developed for the PC but it will run on a MAC using emulation software such as WineBottler.