Carrd - Simple, responsive one-page site creator.
Ethereal by HTML5 UP - A fully responsive side-scrolling one-page HTML5 template
Landing Pages in MailChimp - Easy to build, custom landing pages for free
Mashup Template - Collection of beautiful free HTML templates
Bumble - Bumble is a social network that allows you to feel empowered while you make those connections, whether you’re dating, looking for friends, or growing your professional network. One first move on Bumble could change your life.
HTMLEmail.io - Responsive HTML email templates for startups & developers