OpenToonz is open-source software used by professional studios (most notably Studio Ghibli). It is highly sophisticated and designed for traditional animation production.
Adobe offers a significant discount on its "All Apps" plan for students and teachers. Often, you can get the entire Creative Cloud suite (including Animate, Photoshop, and Illustrator) for over 60% off the standard price. adobe animate free
If you like Adobe Animate because of "tweening" (automatically moving objects between keyframes), Synfig is the closest free alternative. It is vector-based and designed for 2D animation. adobe animate free
Krita is a free, open-source painting program that has a robust animation workspace. While it lacks the interactive/web features of Animate, it is exceptional for traditional frame-by-frame animation. adobe animate free