If you're looking for a Mockey alternative, Mokker is a good choice. It lets you create high-quality product photos with a simple background swap. With over 100 templates, a moodboard option, product replacement and color control, Mokker is geared for e-commerce companies. It also has a free tier with 40 photos and a few paid options for those with different needs.
Another good alternative is Flair. This AI-powered visual editor is geared for ecommerce product photography. It's drag-and-drop interface, templates, real-time collaboration and the ability to combine different design ideas make it a good option. Flair has a free plan with 10 images/month and several paid tiers for different levels of use.
If you're looking for a more general design and prototyping tool, check out Mockitt. It's not a mockup generator, but Mockitt has good tools for prototyping and real-time collaboration. It's got features like AI prototype generation, magic fill and tutorials to help you get started, and it's good for designers and developers.