I build Webinar Signup Landing Pages on a variety of platforms. This one was built using Thrive Themes. It is a very versatile plugin that can be used as an alternative to the more costly Click Funnels software. It is great at handling integration to email marketing programs and offers extensive A/B split testing options.
Thrive themes is both a landing page and website platform and is an excellent choice when a full marketing system is required. Particularly if you want a number of landing pages over various websites and find Click Funnels either too expensive or too complicated to use.