A free program for Android, by StickyApple.com.

WiFi Auto Reconnect is a handy utility that can automatically reconnect your device to WiFi when it goes offline. The app is useful when you need to stay connected to the Internet even when your device is in a bad connection or you are using a mobile data connection with a low bandwidth. 

How can it help me?

When you’re connected to WiFi and you lose your Internet connection, it will automatically try to reconnect to the saved WiFi network you have configured. The app can run in the background to ensure that it will continue to try to reconnect even when the app is not in use.

It will not only help you stay connected but will also save you from having to configure another network manually.