Dia Alternatives

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.

Online diagramming application

Simplify and communicate complex information using data-linked diagrams.

PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.

LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.

Draw, LibreOffice, ODF, open standards, creative software, vector drawing

OmniGraffle is for creating precise graphics like website wireframes, an electrical system designs, or mapping out software class.

StarUML

Gliffy is a powerful HTML5 online diagram maker. Create a flow chart, network diagram, UML diagram, organizational chart or wireframe with ease.

Single-user mockup / wireframing / diagramming tool

Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.

Looking for an affordable software with Enterprise Architecture tool, PMBOK tool, UML tool, Agile tool, BPMN tool and UX tool? Read this page for details.