GDevelop is a lightweight open-source game engine featuring a visual based event system that allows you to express complex game logic without having to write code.
Synfig Studio is an open-source 2D animation app that can be used to produce both vector-based cut-out animation and film-quality animation using bitmap artwork.
Inkscape is a free and open-source vector art editor that uses Scalable Vector Graphics (SVG), allowing your artwork to be scaled to any size without losing quality.