What are some alternatives?
When comparing Page Flows and Terrastruct, you can also consider the following products
UX Archive Animated - iOS apps animated user flows
SnapUp - Wireframe faster / create amazing user interfaces
User Onboarding - Onboarding teardowns of popular sites/services
Plectica - Easily diagram anything, together
UI Movement - The best UI design inspiration, daily
Whimsical Wireframes - Lightning fast wireframing with real-time collaboration.