Coggle is a free mind mapping tool that I started using a couple of years ago when it was in beta. Coggle is a collaborative mind-mapping service. Recently, Coggle was updated to make it easier to emphasize portions of your mind map. To bring attention to a specific part of a Coggle mind map you can now just click and drag the corner of a box in the map to have the font size increase.
To create a Coggle mind map just sign-in with your Google account and click the "+" icon to start your mind map. After entering the main idea of your mind map you can add branches by clicking the "+" icons that appear next to everything you type. To re-arrange elements just click on them and drag them around your screen. You can invite others to view and edit your mind maps. You can also just invite others to view by sending them an email through Coggle. All Coggle mind maps can be downloaded as PDFs or PNG image files. You can also save and organize Coggle mind map files in your Google Drive account.
Applications for Education
Creating mind maps or webs is one of my favorite ways to organize ideas and information. I've often had my students create mind maps as an exercise in making visual connections between important concepts, events, and people in a unit of study.