Wireframe.cc - Sweet and simple online wireframing tool.
OpenToonz - OpenToonz is an animation program that is a free software version of Toonz, the animation software...
WireframeSketcher - WireframeSketcher is a wireframing tool for creating wireframes, mockups and prototypes for desktop, web and mobile apps. It's a desktop app for Mac, Windows and Linux, and a plug-in for any Eclipse IDE.
Synfig Studio - Just another WordPress site
Saola Animate - Easily create engaging HTML5 animations and interactive web content without coding skills
Adobe Animate - Adobe Animate is a Flash, vector animation software.