MINI Nano DSO203 DS203 Professional Digital Oscilloscope 4 Channel 72MS/s
Use coupon code 9061b0 for additional $14.56 off already discounted price for final price of $130.9 (was $193.86, seedstudio still sells them for $199.99)
This is very versatile and powerful pocket piece of open hardware. Alternative firmware and other useful software is available here:
It can even run additional applications like logic level analysers etc. or tetris
Stock version firmware review below: