What I love about TeXnicCenter is that it has pre-defined LaTeX snippets which makes it easy to create complex formula and documentation particularly for computer scientists.
Citations form a major component of scientific documents and TeXstudio provides support for Link overlay helps a lot in that.
Pricing Authorea has 4 pricing plans: Free, Groups, Enterprise.
There are plenty of extensions to TeX, so it can be used to write about any subject, but it is probably noticed the most in mathematics, computer science, and science because it was originally designed to typeset complex mathematical formulas.
It is possible that HTML formatting is supported but has been disabled.
Typically you will want to look for an option labeled "HTML Format" or "Rich Text" in the options section of the client or in the text composition window.
With this tool, you get the same set-up irrespective of location, browser, etc.
The second paragraph has excessive line spacing.