Gemse is currently being ported to modern browsers.
The project Gemse has been started in the need for an editor for mathematical formulas that is fast and can be controlled by keyboard only.
Version 1 of Gemse has been written for Mozilla back in the days when it was possible to write full applications that properly integrate with the host OS as if they were native. Unfortunately, Mozilla decided to get rid of integration with foreign programming languages, the UI description language XUL, and the whole extension infrastructure. After this castration of the Mozilla platform, Gemse stayed unusable for many years. However, web standards have evolved in a manner that allows an application like Gemse to be written for every browser. This will become version 2 of Gemse.
You can track the progress in Gemse's repository on github.
You can find other solutions on the software list of the W3C.