Xamarin.Android - Integrated environment for building not only native Android but iOS and Windows apps too.
Bizness Apps - Create your own app or become a reseller and build apps for others
Rider - Rider is a cross-platform .NET IDE based on the IntelliJ platform and ReSharper.
GoodBarber - GoodBarber is a mobile app creation platform.
RAD Studio - RAD Studio 10.2 with Delphi Linux compiler is the fastest way to write, compile, package and deploy cross-platform native software applications. Learn more.
Fuse - Fuse is a UX tool suite for mobile app designers and developers.