Streetcomplete can filter the map with a variety of filters for features you can edit or complete(Street lighting, Surfaces, Sidewalks, Bike paths, Street parking, Addresses, Places, Things, Buildings). Plus there's some specific "quests" where you can complete information for specific POI ("Does this bench have a backrest? Yes|No", "Where does this fire hydrant lies? On the grass | On the roadway | On a walkway | On a parking).

Mapcomplete also offers filling info about existing POI, but you can filter on specific theme (Drinking water, sports) or very specific theme (etymology) or even your own. There's also an UI to add new POIs; I don't think it's possible with StreetComplete.

Either way both are great.

What does the etymology theme do? Allow you to add the etymologies of place names?

> There's also an UI to add new POIs; I don't think it's possible with StreetComplete.

You can do it in Things and Places layers (layers can be enabled by tapping circle in top-right)