Fuel injection computer and engine management system.
Megasquirt EFI is a range of standalone engine management systems (fuel injection computer, ECU). All systems are intended for DIY install and most installs are self tuned. With Megasquirt you get the opportunity to learn how engine management works and gain full tuneability of your engine. Be sure to read the documentation here and on vendors' sites to see which of the product range is right for you to get the best results.
The main MSEXTRA.COM website has been down all of Wednesday 29th October due to ongoing failures with the hosting company Hostgator. Please try the link to see if it has come back up. In the maintime, the PDF documentation is available below.
Main page describing Megasquirt product range
Read the manuals here