CantonSkill is a free app that provides basic Cantonese lessons similar to, but less comprehensive than, that of ChineseSkill and Duolingo. Rather than expecting you to learn through pattern recognition alone, it provides simple vocabulary and grammar explanations.
The user interface is quite basic, and there are several bugs with the voice recognition. However, even with the limited content available, it has received positive attention for thorough beginner content. If you’re looking for an introduction to Cantonese, this is a great free option.