Computer Architecture of Web Browsers

• JavaScript lets you modify any element of a web page: you can programmatically add text, move images, process and respond to keyboard and mouse input, and talk across the network to a web server.  This lets you build full applications that run right out of an HTML file, in any browser, on any machine from a Windows desktop to an Android Linux tablet.  On most modern browsers, JavaScript runs using dynamic binary translation, so bare arithmetic is actually quite fast.
• WebGL (see Dr. Lawlor demo!) lets you do OpenGL and GLSL graphics card programming directly from your supported web browser.  (Caveats: WebGL support is uneven.  It won't work in Internet Explorer, and some hardware or drivers are 'blacklisted' for executing poorly.)
  
• WebCL will let you do OpenCL parallel programming.  Caveat: support is currently via a semi-mythical plugin.