+1 on StreetComplete. Keep in mind, it restricts contributions to the area you're currently in based on location data. I resorted to spoofing my GPS location so that I could keep contributing :P
Vespucci seems interesting, thanks for the suggestion!
To cover other neighbourhoods in my city that I know well. When I am physically there, I'm usually biking and can't edit real-time, so I do so afterwards at home. I verify all my potential changes and ensure they match what I've seen. I've covered about half my city so far :)