I can't say OnePage Design (short for 'OPD' below) is a no-code tool, but absolutely less-code, it helps users create popular components easily and quickly, it avoids writing the code repeatly. In the back end, you can easily resort the elements, duplicate to other page or export to other sites.
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Use popular responsive framework - Twitter Bootstrap as the core style. Users can easily master it and find themes easily.
Besides the components built by Bootstrap, OnePage has been customized in different screen sizes(Desktop, Tablet & Mobile) itself in order to make the content display smoothly.
OnePage is more like content builder, what you do is to draw the idea into it. So it's good to build a landing page for a site, because it's mobile-friendly.
No, it's under GPN license, so you can use it free. You just buy the update access. If you want to get fast support, you can purchase site tracking service in addition.
Yes, although OnePage is not a no-code builder, you can still use them to make a page. (Ah... a simple page)
Of course, but I can tell you no software can create a really cool page easily as no machine can draw a pretty cool and unique picture, designer is still dominating. Learning some html knowledge can achieve that easily. It's not hard, trust me!