The library hostpolicy.dll was not found

Update for dotnet core 2.0 and beyond: the file appname.runtimeconfig.json (for both debug and release configuration) is needed in the same path as appname.dll.

It contains:

{
  "runtimeOptions": {
    "tfm": "netcoreapp2.0",
    "framework": {
      "name": "Microsoft.NETCore.App",
      "version": "2.0.0"
    }
  }
}

then dotnet.exe exec "path/to/appname.dll" [appargs] works.