What are some alternatives?
When comparing Terrastruct and SnapUp, you can also consider the following products
Plectica - Easily diagram anything, together
Justinmind - Define awesome experiences through wireframes & prototypes.
Whimsical Wireframes - Lightning fast wireframing with real-time collaboration.
Balsamiq Cloud - Fast, approachable, collaborative wireframing
UserGuiding - UserGuiding - Better User Onboarding Without Coding
Method Wireframe Kit - Find your method of being incredibly fast in prototyping.