Recently I used Freemind for a presentation in a bigger conference - life. Much more usable than Powerpoint etc.; for answering questions you could drill down the forks to the details, the non-linear tree structure made navigating much easier. The nodes were text, html, pictures or links - everything that was necessary was possible. No installation needed, just Java and an USB-Stick with the map, the linked documents and a Freemind-runtime-environment to take with me. Very convincing.