Bus Pirate v4 is a universal bus interface that talks to electronics from a computer serial terminal. Get to know a chip without writing code. Eliminates a ton of early prototyping effort with new or unknown chips. Seeed Studio is the official manufacturer and supporter of the Bus Pirate project. Version 4 is the next generation Bus Pirate hardware, but it's not as stable as Bus Pirate v3.
If you're just starting out with the Bus Pirate we still recommend v3 - it's cheaper, more reliable, and has all the same major features. Protocols 1-Wire, I2C, SPI, JTAG, asynchronous serial (UART), MIDI, PC keyboard, HD44780 LCDs, and generic 2- and 3-wire libraries for custom protocols.
USB interface, USB powered
5volt tolerant pins
0-6volt measurement probe
1Hz-40MHz frequency measurement
1kHz-4MHz pulse-width modulator, frequency generator
On-board multi-voltage pull-up resistors
On-board 3.3volt and 5volt power supplies with software reset
Macros for common operations
Bus traffic sniffers (SPI, I2C)
Transparent USB->serial bridge mode
10Hz-1MHz low-speed logic analyzer
Custom support in AVRDUDE,Flashrom,OpenOCD
AVR STK500 v2 programmer clone
Scriptable from Perl, Python, etc.
A bootloader for easy USB firmware updates
Open source (CC 0/public domain)
New in Bus Pirate v4
256K program space, 4 times more flash than v3
Integrated, on-board USB (faster)
Data storage EEPROM to store settings
Software pull-up voltage selection: 3.3volt, 5volt, or external supply
2 extra I/O pins