WebAPI/WebSerial
WebSerial is a suggested API that would provide a way for websites to to read and write from a serial device through Javascript.
The idea behind it is to bridge the web and the physical world, and communicate with devices such as Arduinos, 3D printers, and other Serial devices. This is currently only available to desktop apps, or to websites through the use of insecure and outdated technologies (Java Applets, NPAPI plugins).
Chrome already has an implementation available for Chrome Apps, but by being available only for packaged chrome apps, it's moving further away from the idea of the open web.
Implementation
The WebSerial API could be implemented using the serial library by wjwwood, also used in ROS. It's a very good, open-source, stable C++ library with a clear documentation, and it's MIT-licensed.