Showoff is a Sinatra web app that reads simple configuration files for a presentation. It is sort of like a Keynote web app engine. I am using it to do all my talks in 2010, because I have a deep hatred in my heart for Keynote and yet it is by far the best in the field. The idea is that you setup your slide files in section subdirectories and then startup the showoff server in that directory. It will read in your showoff.json file for which sections go in which order and then will give you a URL to present from.