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.
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.
Adobe Animate, previously Adobe Flash Professional, is an authoring environment (IDE) that can produce interactive solutions for running inside web browsers or for the desktop.
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.
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
Moho has everything you need to make amazing, professional animations. Used in the OSCAR nominated films, The Breadwinner and Song of the Sea, for Best Animated Feature Film.
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.