Calendar

Date picker (use context menu):

Gantt diagram (use context menu):

1. Open a mind map and press ~ (or File Plugins)
2. Find a plugin with name "Calendar"
3. Select it
   

If you share a mind map, other users will have this plugin installed automatically, they don't have to click anything to do it.

For those who know JavaScript.

1. Download plugin
2. Modify the downloaded file in a text editor
   • Also change the plugin name
3. Open a mind map and press ~ (or File Plugins)
4. Select the modified file by the button