The best software modeling/project management tool you've never heard of: PowerPoint
I've found some of the simplest tools to often be the most obvious (can you say
Occam's Razor???)
As an example, if I can avoid using super high-end tools in my software development for UML modeling and/or Gannt chart for project management, I use PowerPoint. It's something I've already got no matter what PC I'm on, and minus the automatic code generation, does the same thing - sight summaries of the work I'm to do.
Don't get me wrong, I enjoy other niche tools, but sometimes less really is more.