What are some alternatives?
When comparing hireframes.com Mobile Sketchpad and Source Wireframe Kit, you can also consider the following products
Whimsical Wireframes - Lightning fast wireframing with real-time collaboration.
Vireflow - A responsive wireframe kit for Webflow
Method Wireframe Kit - Find your method of being incredibly fast in prototyping.
Form Wireframe Kit by InVision - A free wireframe kit from InVision
Contra Wireframe Kit - Open source wireframe kit for design and prototyping 🚀
Wireframe Deck of Cards - A physical way to build and revise website and app layouts