One of the most popular ‘hobby’ projects for people playing around with WebAssembly is creating emulators. This one is a NES emulator (an 8-bit console from the 1980s for those too young to remember), written in Rust using the new native WebAssembly backend.
Once you can compile and run C++ in the browser, anything is possible, and this is a good demonstration that pushes it to the extremes. Here we have the clang compiler, compiled to WebAssembly, running in the browser, allows you to write C++, that is compiled to WebAssembly, client-side. Got it? … Good.
Another Rust demo, with a really good write-up.
And another one … a Rust game, ported to WebAssembly, with a very detailed write-up.
And Finally …
In response to Spectre and Meltdown, Mozilla are turning off support for a few browser features. Let’s hope WebAssembly isn’t next!