Krita

Krita is less than 500 mb to download and install.

FREE unless you want to do so via the AppleStore for £12.99, Windows Store for £12.49 or Steam at £8.50 (prices updated April 2026) for the same product, with the advantage of easier automatic updates and contributing to development costs.

There is also a portable version which allows you to run it from a USB stick or bypass admin password restrictions.

For additional options to render animations, you may want to install an additional small free open-source program called ffMPEG. For details see the manual link here