Overview
Enabling tooltips is a simple but powerful feature. This allows tooltips to show when hovering on a task within the Gantt widget. No additional tab will be shown but a view within the Mendix modeler itself will be shown.
For an example see: tooltips
Implementation
Enabling tooltips is done through the features tab and ensure that you set "tooltips" to "yes". Then define within the modeler what you want to show in the tooltip. This can be achieved with plain text or through Mendix widgets, even with clickable buttons.