Thanks! As I understand it, Tessel uses a version of node.js (and probably Linux underneath) so it needs around 32mb of RAM (and quite a lot of Flash too).

I've worked pretty hard to get Espruino running in 8kb (with space for variables) so that it can run on a single cheap IC (without external RAM).

I think they probably serve quite different markets. I figure Tessel are aiming to provide more of an ecosystem? If I'm honest I think they've got a bit of a fight on their hands against Raspberry Pi/Beaglebone with node.js installed, so I'd guess they're going for some kind of added value.

On the other hand, Espruino's aiming more where the Arduino is. Low power, where you want to play with LEDs or automate a project you've made, and you want the instant gratification of using an interpreter.