userscripts.org, no fancy design but easy enough to understand what is it and what can I do.
Twitter editing profile. After click the button clickable area is easy to understand, non related area turn to transparent.
Youtube comment, show comment field for non logged in user and provide a login link when try to post a comment.
Slack allows you to complete your profile through a "chat", with slackbot :)
Inspiring workspace photos by Julia Manchik
Etsy – When writing a review, the site gently encourages you to the requisite five words and beyond.
Disqus login page. If you hover the social network button, it'll get a little bigger.
Medium "Verified Email" page. The animation is really cool, jumps from bottom. Like the big overlay to put background behind and make the real content pop up.
Medium blank bookmark page.