I investigated trying to use Doppio for Peergos. It is a very cool project. In the end we decided against it because it wasn't fast enough for our use case yet,

I investigated trying to use Doppio for Peergos. It is a very cool project. In the end we decided against it because it wasn't fast enough for our use case yet, and it requires the page to download the whole JVM (at least the rt.jar - the runtime) which is >60 MiB. We managed to get around this by manually stripping out the parts of the JVM that we didn't need, which brought it down to a few MiB. I imagine that once they update it to Java 9 with the modular JDK (and resultant splitting of rt.jar) this reduction will largely happen automatically with it lazily downloading the parts that it needs.