If you're a dev who wants to be able to sign multiple apk and zip files very quickly and effortlessly, check out XDA forum member olboss's Windows tool.

The auto-signing tool is a GUI application based on signapk.jar for Windows, and can sign multiple apk and zip files very quickly in one click. It also features a drag and drop function and supports signing with privatekey.pk8 and publickey.x509.pem.

The tool can also sign a mixture of apk and zip files together - you just need to extract the archive the dev has provided, launch, select your files and then click on 'Sign files'.

For more information and to download the tool, head on over to the application thread.