I can recommend the DigiSpark as a cheaper, slower, alternative that works with the Arduino IDE [1]. Somebody could easily get it into a smaller form factor.
I've bought some of the official versions in their KickStarter and whenever I buy through some company/research funding - but can also recommend the cheaper Chinese implementations to be just as good for projects.
>That doesn't fit entirely within the USB port like the Tomu,
No, but it would be possible to get something more low profile with some work. For most projects I would imagine it's low profile "enough".
For a practical joke (because I'm cool/evil), I plugged one of these devices into the back of somebodies desktop PC and it would occasionally output a random character (either G, H, J or K). I thought the same would be amusing for mouse control too.
You can get it to ultra-low power states too if you replace the power drop down (which consumes about 10mA from memory) and build a low power monitoring device.
>and it's out of stock (with no eta).
That's a shame. Erik is currently working on a 3D printer, it's likely this takes up most of his time now [1].
I've bought some of the official versions in their KickStarter and whenever I buy through some company/research funding - but can also recommend the cheaper Chinese implementations to be just as good for projects.
[1] http://digistump.com/products/1