E-Gates are a program where the traveller has been heavily vetted by the UAE Authorities and a special card is issued allowing the user to clear customs at an automated Kiosk using a fingerprint rather than lining up and talking to an agent. E-Gate is only available to UAE citizens and residents and a few selected other categories. It is similar to Global Entry / EasyPass / Privium / Australian SmartGate.

SmartGate (UAE) is like the APC (Automated Passport Control) kiosks in the USA, whereby the implantation in the UAE allows all passport holder of Visa-Waiver or Visa-on-Arrival nations to use the SmartGates to electronically clear customs as well. And, like the US APC (not GlobalEntry) program, you do NOT need to pre-apply or have any special membership to use it.

And, much like entry to the US, you may be asking "what is the advantage of E-GATE over SmartGate - it looks like the same thing". Well, that may be true at the moment but as more and more people get shunted through the SmartGates, the queues will become longer and the advantage of E-Gates being a vetted program and thereby having shorter lines will re-emerge.

Also you can use the E-Gate system for departure customs clearance as well while there are no SmartGates installed for that purpose.

So for the moment it seems like E-Gates and SmartGates are essentially the same thing with E-gates promising faster clearance due to potentially shorter lines and also due to the vetting you have received when signing up for the program.