Collapsible Groups (Grouped Items)
BCGControlBar Pro (MFC)
BCGSuite (MFC)
BCGControlBar for .NET
The Gantt Chart supports item's hierarchy, which allows grouping of tasks that logically belong to one project.
Sample code:
pItemGroup = new CBCGPGanttItem;
pItemGroup->SetGroupItem(TRUE);
pSubItem = new CBCGPGanttItem;
pSubItem->SetHierarchyLevel(1);