The Broadway HTML5 back-end was merged into GTK+ 3.2 although this web back-end for GNOME's tool-kit hasn't seen any major deployments yet. Broadway though has advanced with features while living in GTK.
Alexander Larsson, a developer working on GTK+ and Broadway, has shared that there's now multi-process support. This basically allows for running multiple GTK applications within the web-page. "I just landed support for multiple processes in broadway. The way it works is that we run a process (broadwayd) similar to the X server, which all broadway apps talk to. Additionally it has a webserver built in that the browser connects to. This allows (for instance) broadway processes to start other broadway processes. Basically the webpage turns into something like an X session."
Larsson shared this news via his blog. For showing this off, he's created a video demo of the Broadway GTK+ improvements, which is embedded below.
GTK Broadway commits can be found via the GNOME.org Git log. This feature will be part of the GTK+ 3.8 release.