The ClarisImpact box states: "...Manage projects using Gantt charts with customizable plan/actual task bars, milestone markers..."
ClarisImpact 1.0 does not contain a milestone marker feature, and the terms "milestone" and "Gantt" are not used in the product's electronic help. Although "Gantt" is not listed in the index, the ClarisImpact User's Guide describes Timelines beginning on page 8-2 as follows: "ClarisImpact creates simple timeline charts that are suitable for scheduling and tracking a wide range of projects. Timelines, also called Gantt charts, represent task durations as bars on a time scale."
A milestone, as described in the Claris MacProject Pro manual, marks a phase of a project. "Milestones typically mark the beginning and end of a project and any interim goals for a phase of the project or a set of tasks. They serve as visual clues for significant progress points along the way."
To create a simple milestone in ClarisImpact, it is possible to define a task with zero duration. This will appear as a small shape (diamond, circle or another shape that you might select) in the timeline, not as a line like other tasks.