Surtitle - Have you heard of those?

I recently had an opportunity to work for a stage play. It was interesting and had its challenges but I would stick with movie making any day (no disrespect to theater; in fact I developed appreciation for theater after that.) Anyway, what I learnt was that it was possible to display something similar to subtitles and those are called surtitles or super titles! Here is an opensource software that offers this capability: http://subtitles.nova-cinema.org/home.en.php
Let me know if you know of any other tools - better yet let me know of opensource tools that can be used in subtitling movies.