FlashScan v2 is a tool that allows you to connect to your truck
EFI Live has a few different software applications, one of those applications allows you to download the stock tune on your ECM and make changes to individual tables as you need for your truck. This is more complicated then the average user cares about though. The average user will only use this to flash in tunes created by EFI Live tuners.
EFI Live Tuner - This is someone that creates custom tunes for your truck based on what your specific needs and desires are.
EFI Live is only as good as your tuner, so selecting a tuner is an important decision that shouldn't be taken lightly. You should never select a tuner based on price (high or low), but based on their abilities.
EFI Live with a good tuner is better then a canned tuner that is a generic tune created for all trucks of your specific model. It doesn't account for mods, specific needs, etc...
EFI Live is not right for everybody, but do to it's flexibility it is right for a lot of people. It sounds complicated, but is as easy for an end user as any other tuner on the market IMO.
Read the EFI link Jesse posted and check this link out as well.