OpenToonz is an animation program that is a free software version of Toonz, the animation software used by Studio Ghibli, amongst others.
Synfig is a free and open-source, industrial-strength, vector-based 2D animation app designed for producing feature-film animations. It eliminates the need to create animations frame by frame. It is available for Windows, Linux, and macOS.
Enve is a free and open-source 2D animation app. It can create both vector and raster animations and even use sound and video files. It has been created with flexibility and expandability in mind.
Pencil2D is an opensource animation/drawing software for Mac OS X, Windows, and Linux, based on old Pencil software. It lets you create traditional hand-drawn animation (cartoon) using both bitmap and vector graphics.
Storyboarder makes it easy to visualize a story as fast you can draw stick figures. Quickly draw to test if a story idea works. Create and show animatics to others. Express your story idea without making a movie.
Animation Desk is a perfect tool for animating, storyboarding, and sketching. It’s an app Loved by professional and amateur animators, Youtubers, and many art lovers. Draw you frame-to-frame animation from scratch, or create animations upon videos, images, PSD layers.
Tupi is a design and authoring tool for digital artists interested in 2D Animation, fork of the KToon project, offering an interface experience focused on 8-100 years olds.
TVP Animation is the leading paperless drawing and animation tool, able to imitate traditional techniques such as Pen Brush, Gouache, Watercolour, Pencil, Felt-tip and Airbrush, and animate them over frames.
Pencil is an animation/drawing software for Mac OS X, Windows, and Linux. It lets you create traditional hand-drawn animation (cartoon) using both bitmap and vector graphics.
Updated project here: Pencil2D