Are you thinking of playing the Engineer battleframe in Firefall
? If so you'll want to log in between August 15th and August 18th to take advantage of Red 5's
Accord Engineer Battleframe Weekend. You'll get a 25 percent XP boost and you'll get to goof around with all those spiffy deployable devices.
The "Engineer excels at locking down an area and providing a safe location for its allies to resupply, " according to Red 5's announcement post.