What are some alternatives?
When comparing Flowchart.com and Dia, you can also consider the following products
Unifosys OrgDoc - OrgDoc is a unique desktop-based Organization Chart Creator & Data Organizer software.
draw.io - Online diagramming application
OrgWeaver - OrgWeaver is a cloud-based organizational chart software.
yEd Graph Editor - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.
Visio - Simplify and communicate complex information using data-linked diagrams.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.