If you're looking for a Shortbread alternative, ComicsMaker.ai is worth a look. It's got a broader collection of AI tools to create comics automatically, including a Page Designer, Text to Image, and Character Training. With different pricing levels and the ability to download comics as PDFs or CBZs, it's good for both casual and serious comic creators.
Another good alternative is AI Comic Factory. The service, hosted on Hugging Face Space, lets you create comics automatically with a variety of styles, layouts and engaging captions. You can also upload your own images to customize the look of your comics, so it's good for people who want to get creative.
If you want something more immersive, Custom Story Creator offers an AI-powered site to create graphic novels and comics with sophisticated AI technology. It can handle multiple languages and comes with an XR Reader app for augmented reality/virtual reality experiences, so it's good for people who want to reach a global audience.
Last, Neural Canvas is a simple way to create photorealistic comics with a variety of styles and characters. At $3.99 for a 25-illustration comic book, it's cheap enough to let you try your hand at creating something with AI.