What are some alternatives?
When comparing Terrastruct and FlowMapp, you can also consider the following products
SnapUp - Wireframe faster / create amazing user interfaces
Really Good UX - A library of screenshots for UX inspiration
Plectica - Easily diagram anything, together
VisualSitemaps - Autogenerate visual sitemaps in seconds.
Whimsical Wireframes - Lightning fast wireframing with real-time collaboration.
DYNO Mapper - Create Sitemaps with the DYNO Mapper Visual Sitemap Generator.