Simple. Useful. Light.
I'm not sure if it's because it's Java-based, but I'm frustrated by the lack of normal Windows behavior in ProjectLibre. Cntrl-S does not save, Cntrl-X does not cut (it just copies to buffer, the Cntrl-V pastes but leaves original cell as it was), ESC doesn't exit out of dialog boxes, arrow up/down moves the cursor sometimes but not always, highlighting several task rows and choosing to "insert" doesn't insert several rows but instead just adds one (and at unexpected spots), moving/copying a task to an existing summary task does not adjust predecessors for existing tasks in that summary task. Most of this I think is related to it being in Java (would it be that much harder to build for Windows too? I know, easier asked than done...) It's all just a bit too messy to recommend. However, considering that it's free and Project starts at 600 dollars, I'll keep suffering through for at least my current project, since feature-wise it does seem fairly on par with Project.