Features:
ELM327 USB is the latest PC-based scan tool. It supports all OBD-II protocols and is dispatched with a number of compatible programs. The processor is an ELM327 USB. The output protocol (connection to laptop) is USB. 
Processor: ELM327 USB

OBD-II Protocols: 
• ISO15765-4 (CAN) 
• ISO14230-4 (KWP2000) 
• ISO9141-2 
• J1850 VPW 
• J1850 PWM

Output protocol: RS232
Baud rate: 9600 or 38400
Indicator LEDs: OBD Tx/Rx, RS232 Tx/Rx, Power
Operating voltage: 12V, internal protection from short circuits/overvoltages
Nominal idle current: 45 mA

Description: 
OBD-II Software for ELM327 USB is a free program that allows you to use your PC and a hardware interface to get the information from your car's computer.

The program is very user-friendly, and easy to learn. It is also very easy to install: simply extract the files into a folder on your computer's hard drive, and you're ready to go. To uninstall the program, simply delete the entire contents of the folder where the program resides.

The software supports two platforms - DOS and Windows.

The program lets you perform the following operations:
• Read diagnostic trouble codes, both generic and manufacturer-specific, and display their meaning (over 3000 generic code definitions in the database).
• Clear trouble codes and turn off the MIL ("Check Engine" light)
• Display current sensor data, including: 
• Engine RPM
• Calculated Load Value
• Coolant Temperature
• Fuel System Status
• Vehicle Speed
• Short Term Fuel Trim
• Long Term Fuel Trim
• Intake Manifold Pressure
• Timing Advance
• Intake Air Temperature
• Air Flow Rate
• Absolute Throttle Position
• Oxygen sensor voltages/associated short term fuel trims
• Fuel System status
• Fuel Pressure
• Many others...

Upcoming Features: 
• Data graphing and logging
• Freeze Frame data
• Continuous and Non-Continuous Oxygen Sensor test results

Free software: 
Scantool.net 
• GM Mode 22 Scan Tool by Terry 
• OBD Gauge for PalmOS and Pocket PC by Dana Peters 
• OBD Logger by Jonathan Senkerik 
• OBD-II ScanMaster by Wladimir Gurskij (ScanMaster 3.52 - local copy) 
• obd2crazy.com 
• OBD2 Scantool by Ivan Andrewjeski 
• OBDII for ELM322 by David Huffman 
• pyOBD by Donour Sizemore for MacOSX and Linux 
• RDDTC by Pete Calinski 
• Real Scan by Brent Harris 
• ScanTest for Pocket PC by Ivan Ganev aka a-ser 
• wOBD by WDT