The main one I use right now is Draw Things, and it's pretty great. It's completely free, and I've been able to make some great stuff with it. My question is: are there any other apps out there as good as Draw Things? Apps that are 100% free and don't require signing up?

Here are some pics I made:

                                               

Draw Things is unique because it runs a fully functional version of Stable Diffusion on your own device. For technical reasons, there's nothing like it available on Android. Most AI apps from the App Store/Play Store run on the app developer's server as a paid service, and have nsfw filters as per the Store Ts&Cs. 

There are other projects to run Stable Diffusion locally on iOS, but afaik Draw Things is more developed.