I tried Projectlibre, and while it can more or less do what’s required in terms of putting events on a timeline, it doesn’t have the same visual presentation possibilities of PowerPoint. If nothing is available I can use PowerPoint online, but would prefer an offline solution.
Have discovered they are called Gantt Charts. Tested a number now, but none offer the kind of flexibility I’m after. They are suitable for fixed calendar schedules with precise dates and two word descriptions, whereas I need only a generalised timeline and text box descriptions. Might have to draw something up in inkscape, or Libre Office.
Look for roadmap charts instead of Gantt Charts.
Both are more or less the same. I’d say roadmaps are more a high view of a project and Gantt Charts more detailed.