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.<p>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.