The list given below gives links to some open source software. As these lists could include some proprietary software also, please make sure that the software you choose for the Hackathon is indeed open source. Please note that in general free of cost software and software that are free for students and faculty need not be open source software. Make sure that you select ONLY open source software. The following list is only a sample. There are many more open source software not listed in these links. Some questions on the Hackathon Registration/Proposal Form will give an idea of how your proposal will be judged.
One can learn Scilab through Spoken tutorials available here.
You may want to watch four short videos given by Prof. Kannan Moudgalya about Scilab and its benefits. Click here to watch them on YouTube.