Let’s assume we want to mock up screens of an app. What except well-known draw.io can we find?
First of all, they’re called “wireframes”, not “mockups”. A mockup is some mock with your text on anything from cups and T-shirts to ad-shields. So, free tools to create wireframes:
https://wireframe.cc/ : minimalistic, but we have to save urls of our works.
https://mydraft.cc/ : controls included, yet we have to save urls still.
https://pencil.evolus.vn/ : desktop, free and open source.
Miro: has 3 boards for free. Unlike many others with a single project.
JustInMind tool: desktop, for mac and win only.