Lurch is a word processor
It is also much more, but it is a word processor.
While its main goal is to be able to check the reasoning in students' mathematical arguments, its foundation is a word processor. A copy of the Lurch application is embedded below. You can see that it has all of the basic word processing functionality, including headings, fonts, and so on.
Under the hood
Lurch is built on the pre-existing, open-source project TinyMCE, which is used in literally millions of other web-based projects. It is a mature product that is easy to extend with new functionality, which enables us to build Lurch with TinyMCE as the foundation.