You can turn off signing checks for kernel extensions.

Zinio has released a version of their iOS app for iOS 5 outside the app store. You went to their site on your iOS device and it downloaded and installed the app. I think it was done using Enterprise certificates, but I'm not sure.

As for iOS apps, you can compile and run iOS apps on your own device without the need for a signing cert.

There are apps for iOS that allow end-users to program their own devices. For example, Pythonista:

http://omz-software.com/pythonista/

Plus, Swift Playgrounds gives access to the whole iOS SDK.