The best free alternative to Lucidchart is diagrams.net, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 100 alternatives to Lucidchart and loads of them is free so hopefully you can find a suitable replacement. Other interesting free alternatives to Lucidchart are Dia (Free, Open Source), yEd Graph Editor (Free), LibreOffice - Draw (Free, Open Source) and Freeplane (Free, Open Source).
my.origramy is an online service that lets you create any complex graphs, presentations, schemes - anything you want - for free. The background of the service is the Origramy flash editor/viewer component.
Wireframe your Ideas iPlotz allows you to rapidly create clickable, navigable mockups and wireframes for prototyping websites and software applications. Create a project, add wireframe pages with design components and discuss your creations with others.
A digital workplace where your team can collaborate from anywhere in the world. Visualize your ideas on the Online-Whiteboard in realtime and easily track your working hours with the intuitive Time Tracker.
ClassBuilder is freeware CASE tool targeted at the C++ developer, running on Win2K-XP. It lets you create, manipulate and navigate classes, class relations, class members and class methods at a high level of abstraction through a graphical user interface.