When comparing Instapage vs RocketCake, the Slant community recommends RocketCake for most people. In the question“What are the best WYSIWYG website builders?” RocketCake is ranked 4th while Instapage is ranked 7th. The most important reason people chose RocketCake is:
You can work offline as RocketCake is an installable Windows or Mac application. It's also possible to publish on a local disk first before uploading to a webserver.
Specs
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Pros

Pro Mobile-friendly
The auto-mobile feature means that any page you build, will automatically be viewable on any mobile device automatically.

Pro Easy to get started
There are three easy ways to get started. You can use the drag and drop editor to build your own page from scratch or customize a template. You can also import current web pages and edit them in the drag and drop builder.

Pro 100+ templates
There are over 100 ready to go templates for lead generation, webinar registration, mobile apps, and thank you pages. There are new templates constantly added as well.

Pro Built-in tools for A/B testing
Pro Offline
You can work offline as RocketCake is an installable Windows or Mac application.
It's also possible to publish on a local disk first before uploading to a webserver.
Pro Wysiwyg
No need for coding.
Pro Mobile support
Support for e.g. iPhone 8, iPhone 7+, iPhone 8+, iPhone X, Samsung Galaxy S8, Galaxy S8+, LG G4, LG G5.
Pro PHP and ASP support
It's possible to use PHP or ASP to create dynamic websites.
Pro Templates
15 free templates to choose from.
Cons
Con Web-based, not a proper application
Con Limited to landing pages
Instapage focuses on creating simple, static lead generation and click through landing pages.
