There's Beaglebone, Raspberry Pi, and also now Tessel that do that. The previous two have had node.js support for ages but I think have been lacking any kind of real advertising because they're more general purpose.

All of those appear to be fully-fledged computers though, and Espruino's not really aiming to compete with them.

Instead, you get to use JavaScript on a very small, low-power microcontroller than will sensibly run off a small battery for days on end.

Some people will want one thing, some will want another - and hopefully they can both coexist. If we get it right they'll both help each other and we can end up with a large library of JavaScript code for embedded devices :)