I've got a few experimental new "Slave Plugs" for people who want to experiment with adding one or two additional ATTiny's to a JeeNode via any of its 4 ports. The idea is to have these slaves act as I2C slaves, this will require some code. Each slave has a 6-pin header connected to it to interact with the outside world (3 I/O pins) - the pinout is such that each slave could emulate a full port and drive other plugs attached to it. Some uses which come to mind are: servo control, PWM outputs, stepper control, LED matrix displays, ...
Board layout and schematics can be found here: http://wiki.jeelabs.net/p/32
I'm probably not going to be able to work on this soon (I'm swamped!). Contact me with details if you want one of these "raw" plug boards (no chips included, no software) and I'll send it off. If you need one with an ATTiny85 soldered on, that would be possible too. Keep in mind that you'll need to hook up an ISP programmer to flash these things.