[mlni]

There are a bunch of these four-wheel bikes (https://vokbikes.com/) rolling around where I live. They're meant for commercial use and are slow enough for sidewalks and they do have a roof covering the rider. Cost more than $2000 though.

[driverdan]

Four wheel bikes are technically illegal in some places. Texas, for example, considers anything with three or more wheels a motorcycle or car and requires that it be registered.