StreetComplete: Easy to use editor of OpenStreetMap data
I can recommend installing this and opening it while you are bored on a walk somewhere through your city. The questions are very well phrased, come with intuitive pictures to help you answer.I'm not sure how useful the edits are in practice but I've contributed hundreds of questions about wheelchair-accessible  sidewalks, street lighting etc and hope that this is helping some people make better navigation decisions.