The best open source alternative to ConceptDraw DIAGRAM is Excalidraw. If that doesn't suit you, our users have ranked more than 25 alternatives to ConceptDraw DIAGRAM and ten of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to ConceptDraw DIAGRAM are LibreOffice - Draw, Pencil Project, Dia and vym.
Excalidraw is an open-source whiteboard tool that lets you easily sketch diagrams that have a hand-drawn feel to them. Available directly online as a web app and also through CodeSandbox to easily see how the code works, and the app is available for self-hosting.
Draw lets you produce anything from a quick sketch to a complex plan, and gives you the means to communicate with graphics and diagrams. With a maximum page size of 300cm by 300cm, Draw is a an excellent package for producing technical drawings, general posters, and much else.
Pencil is a standalone app that lets you create diagrams or UI mockups. It doesn't have collaboration/multi-user features.
Open-source diagram editor supporting Linux, Windows, Unix, and Mac OS X, with features for constructing entity relationship, UML, flowchart, and network diagrams, customizable with XML-defined shapes, extensibility, and a GTK+-based graphical user interface.
VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts. Such maps can help you to improve your creativity and effectivity. You can use them for time management, to organize tasks, to get an overview over complex contexts, to sort your ideas etc.
Feature-rich, open-source Wireflow offers a collaborative platform for online creation of complex user flow prototypes. Ideal for team work in UI design, wireframing, and mind mapping, promoting idea sharing in real-time environment aided by modern whiteboard features.
ProcessMaker is a cost effective and easy to use open source business process management (BPM) or workflow software application.
Diagramo is an online flowchart software
PathVisio is a free open-source pathway analysis and drawing software that allows drawing, editing and analysing biological pathways.
Core2D is a multi-platform application for making data driven 2D diagrams. The application has built-in wyswig vector graphics editor where you can bind data to shapes, share data across multiple documents, edit documents using layers.
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