What are some alternatives?
Devise - Flexible authentication solution for Rails with Warden.
Proto.io - Create fully-interactive high-fidelity prototypes in minutes that look and work exactly like your app should. Sign up for a free 15-day trial and get started.
SquareSpace - Squarespace is the easiest way for anyone to create an exceptional website. Pages, galleries, blogs, e-commerce, domains, hosting, analytics, 24/7 support - all included.
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project
Satellizer - Satellizer is a nd-to-end, token-based authentication module for AngularJS
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.