A guildy was interested in the Engineer profession. I wanted to gather as much information as I could for him. Credit again to Beliasta.

Engineer

Profession Mechanic
Engineers have a tool belt where the F1-F4 skills are determined by the 6-9 (healing+utility) skills, which in effect gives the engineer 14 skills. The engineer is therefore the only profession that can customize their profession mechanic skill-set.

E.g. Having a turret in the 7 skill will give the you the option on the tool belt (F2) to detonate it. Having a flamethrower in the 8 skill will turn the F3 skill into Incendiary ammo and so on.

Turret tool belt skills are useless unless the turret is active, while the rest can be used regardless of their parent skill’s on/off status.

Weapons
Engineers can only choose from technological ranged weapons(inc. speargun) and the shield. They only have access to one weapon set at a time and cannot switch. This of course means that like the Elementalist, the Engineer also has access to a lot of alternate skills. More on that later.

Rifle: Mostly a long ranged weapon though it can punish close ranged attackers if necessary.
Pistol(main hand): Fire special ammo that inflicts various conditions. Close to mid range
Pistol(off hand): Fires an AoE immobilizing agent and can also SET PEOPLE ON FIRE.
Shield(off hand): Creates a forcefield that damages and knocks back enemies as well as reflects projectiles. That was one skill. The other electrifies the shield and stuns attackers. It might do more but I haz no infoz.

Healing
You start with:

Elixir H(30s cooldown): Heals you and gives you either protection, regen or swiftness. F1 throws it at allies for a similar effect.
Med Kit(0s cooldown, 1 skill points): This is a kit that replaces your weapons and gives you 3 drop bandages(heals), 1 drop-condition-removal and 1 drop-fury-swiftness-boon. Running over these drops gives you or allies its effect. F1 heals you (20s cooldown).
Healing Turret(10s cooldown, 4 skill points): Deploy a turret that heals you and then gives regen AoE. Use the skill again for more healing and reviving allies (30s cooldown).

Utility Skills Engineers have access to turrets, kits, elixirs, as well as a few gadgets. GO GO GADGET ROCKET BOOTS. Only profession to not use signets.

Elixirs generally give boons and condition removal to the engineer. Tool belt skills are to throw them at allies for similar but alternate effects.

Turrets are immobile uncontrollable pets that generally do one thing. Use them again to overcharge them and make them do another thing or the same thing but better! Their tool belt skills destroy the turret damaging nearby enemies. The engineer can also pick them up by interacting with them, which is an alternative to blowing them up (you might want to pick them up for example in a coal mine).

Kits are of both Weapon and Device nature. They give very different but still somewhat related skills to the tool belt. Using them replaces your weapon skills. Use the skill again to deactivate them and return to your default weapons.

Kits

Elixir Gun: Fires a large amount of AoEs that give conditions to enemies and boons/condition removal to allies. Tool belt heals you and allies.
Flamethrower: It’s a flamethrower. It shoots fire. Lots of fiery AoE’s as well as pushes and pulls. Tool belt gives you burning bullets for weapons.
Tool Kit: Gives you a wrench. Closest thing to a melee weapon. Tool belt throws wrench and despite the laws of aerodynamics, it returns as well, striking foes along the way.
Mine Kit: Throws mines that you can detonate. Tool belt destroys all mines. This is so that in future, they don’t remain lying around for civilians to detonate.
Bomb Kit: Place a variety of bombs at your location that explode after a few seconds. They are of damage, burning, dazing, blinding, immobilizing variety. Tool belt puts a giant bomb that damages and knocks back.
Grenade Kit: Gives you a variety of ground targeted AoEs that do damage, bleeding, blinds, chills and poisons. Tool belt allows you to throw several grenades at once.

Elite skills

Supply Crate(180s cooldown, 15 skill points): Summon a supply crate from uhhhh…Anyway it does damage/stuns and creates 8 bandages, a healing turret, net turret and flame turret. They can’t be detonated but will likely benefit from turret traits.
Elixir X (150s cooldown, 20 skill points): Randomly gives you the elite forms of Plague, Rampage or Tornado. What the hell is in those elixirs…
Mortar (120s cooldown, 25 skill points): Creates an enviromental weapon that is also a mortar :o. Gives you 5 ground targeted AoEs that damage, bleeds/cripples, heals allies, chills foes, knock back enemies.

Traits
Engineer traits perform as expected and their names tell you a lot about their usage.

Explosives: raises power and condition duration: traits benefit explosions.
Firearms: raises precision and crit damage: traits benefit rifles/pistols/speargun.
Inventions: raises toughness and healing: traits benefit turrets and shield.
Alchemy: raises vitality and boon duration: traits benefits elixirs and healing.
Tools: raises conditon damage and reduces tool belt recharges: traits benefit kits.