Seeed Studio repurposed parts for cheap MP3 players and made a production miniature oscilloscope, the DSO nano. I like this small tool and bought one of the first iterations (see image above). It’s been so popular, it even has it’s own cheap knock-offs (e.g.).

They followed up with the handsome DSO nano v2.

Most recently, they have a beta run of the DSO Quad.

Also an option is the even smaller XMEGA Xprotolab.

Check out how small it is.

Most of these devices are quite slow, 2 MHz or less, but for many signals, that’s fine. Since they’re based on CPUs like the ARM Cortex M3, they have a lot of nice features, like storage, built-in test signals, and a configurable spectrum analyzer mode. Interestingly, they’re also open source, so you can modify the user interface as you see fit.

Hat tip to CW.