ShellMS is the simplest and easiest ADB Shell Messaging Application. If you don't know what ADB or SDK is you definitely don't need this app. For the others it's useful tool to speed up messaging when you're working on your computer.
Although APK downloads are available below to give you the choice, you should be aware that by installing that way you will not receive update notifications and it's a less secure way to download. We recommend that you install the F-Droid client and use that.Download F-Droid