Like GanttProject, OpenProj is an open-source project, and has the potential to be the most popular among the project management software on this list, mainly because of its compatibility with Microsoft Office Project files. (According to the Web site, OpenProj has been downloaded over 1,250,000 times.) It comes as a desktop program in versions for Windows, Mac OS X and Linux.
OpenProj works well on its own for building project plans. Serena Software can offer this application free of charge because makes its money by selling back-end, server-side features to go with OpenProj for business clientele needing multi-projecting, reporting, time sheets, notifications and other enterprise-level apps.
The first thing you'll notice is its extensive charting features. OpenProj features Gantt and PERT charts, and also incorporates WBS, RBS, Earned Value costing, and a few other charting methods. Like GanttProject's PERT charting interface, the tasks and resources in the PERT, Work Breakdown Structure (WBS) or Risk Breakdown Structure (RBS) charts of OpenProj are manipulated by simply dragging and dropping boxes; the pathways among them then reroute automatically.
The way which OpenProj shows you Gantt charts falls somewhere between Gantter.com's clean, simple look and jxProject's layered, visual complexity. OpenProj aims for a visual balance between these two. In its default settings, it labels its task bars with the name of the corresponding resource, and does so with an overall look that isn't as busy or overwhelming as jxProject's. You can also click on a bar and drag it side-to-side along the time line to place it earlier or later in the schedule, as well as adjust the sides of the bar to shrink or stretch the time duration of the task.
Like jxProject, OpenProj lets you assign tasks with work times that run for less than one hour -- down to one minute.
But OpenProj is missing the one user interface feature that I really like in GanttProject, in which clicking a task bar highlights the corresponding name in the task list. (jxProject lacks this feature as well.) I hadn't realized how truly helpful this was until I went over the details of my project as rendered in OpenProj to mentally check off and review the task steps in my project, from start to finish.
A last big plus for OpenProj is that it successfully opened every plan file saved in the Microsoft Office Project format that I used in these tests. The other project management applications on this list usually had problems importing Office Project files, if they had the ability to do so directly at all (without the need to first export the file to XML).