Klavaro is completely free and open source (GPL). It supports multiple keyboard layouts (QWERTY, AZERTY, Dvorak) and does not require registration. For a charity with old computers, Klavaro is lightweight and safe. The interface is less "flashy" than Pro, but the muscle memory training is identical.
If you do not qualify for a charity license, TypingMaster offers other ways to access the software: Free Access | Multiple Ways to Get It - TypingMaster 12 typing master pro charity license key