To create diagrams, I use two main a few different tools.
Diagrams
Lucidchart - basically the closest I can get to Visio whilst using a mac. Yes, I like it so much that I pay for it. I douse Lucidchart for:
- ERD Diagrams
- Swim Lane Diagrams
- Simple flowcharts
(yes, I would like to use one of the tools that integrates with Confluence, but they just don't cut it with some of the visio-like features of layout and snapping).
(yes, you can do sequence diagrams in Lucidchart, but why, when there are much easier ways to create them - automatically).
Graphviz is the tool of choice for flowcharts - see my tutorial about using it in Confluence (unless you use Confluence On Demand).
For sketching out flowcharts on the iPad, I LOVE LOVE LOVE Instaviz
Mockups
Balsamiq for Mockups and Wireframes where necessary (yep, paid for that too). and
For prototyping quickly on the iPad I love Adobe Proto (yep, bought that one too, but it is no longer updated).
Sequence Diagrams
Sequence diagrams for quickly and easily documenting a processs.
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But I use Plant UML and the excellent plugin for Sublime Text (yep, I paid for Sublime Text too - see Mavens Mate MavensMate and Git for Non Developers as to how I use Sublime Text for Salesforce work).
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And no, I am NOT strict about my UML conventions (see the diagram I made for Building a "Simple" Case WorkflowManagement Process), just enough to show the client what is possible.
Graphviz is the tool of choice for flowcharts - see my tutorial about using it in Confluence (unless you use Confluence On Demand).
For sketching out flowcharts on the iPad, I LOVE LOVE LOVE Instaviz and for web prototyping quickly I love Adobe Proto (yep, bought that one too, but it is no longer updated).