A free program for Android, by AppWork GmbH.

Remote for JDownloader is an app that enables you to use your Android device as a remote control for your desktop. It lets you do anything a normal Android device can do, such as browsing the web, sending and receiving text messages, and making voice calls. It also gives you the option of starting and stopping downloads, as well as the ability to pause and resume them. It can even be used to stop and start downloads on your desktop. All you need is an Internet connection on your Android device and the app, and you're good to go.

You can use this remote control for JDownloader on any desktop PC that is running the JDownloader application.