MATLAB is used for a range of applications, including video, image and audio signal processing, modeling of data, etc.
Python (together with NLTK) is used principally for natural language processing and subsequent information retrieval/ data mining.
R is used for statistical analysis of data (or generating synthetic data).
Free and open source toolboxes for classifiers such as support vector machines, artificial neural networks, etc. are used on a need-based basis.
User interface design using various web technologies are used for projects that require significant user-interaction or an elaborate user interface.