Zoom R8

Zoom is a producer of effect processors as well as recorders. 

The above shows a Zoom R8. It is a shrunken version of its big brothers R24 and R16. Actually, R24 and R16 aren't that big. But R8 is even shorter than your 30cm ruler. It is small enough to fit into your guitar bags and it is lighter. It allows you to record your jamming sessions. Best of all, it allows multi-track recording without a computer.
It has a built-in drum machines (like many Zoom pedals do) and you can adjust the audio settings of your track. It also has a few built-in guitar effects to please the guitarists. And like many other records/pedals with recording function, Cubase LE 5 DAW software is bundled together with it.

But.. the smaller something gets, the more complicated the controls are. -.-" Well, nevermind. There is always a manual for reference!