Exalted

Exalted is a triggered ability first introduced in Shards of Alara and also featured in Conflux and Alara Reborn. It returned in Magic 2013 and Modern Horizons. Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn for each creature with exalted.

History
The mechanic was created by Brian Tinsman.

Exalted was introduced in Shards of Alara as the White-dominated shard of Bant mechanic, and was reprinted in Magic 2013 on black creatures, and in Modern Horizons on a red creature.

Later, Design experimented with an "advanced exalted" for Amonkhet, where a creature with the ability granted things other than +1/+1, mostly creature keywords. Then they tried a variant of this mechanic, where a creature with the ability granted a creature keyword to a target attacking creature. It no longer required the creature to be attacking alone, but the creature granted the ability had to be attacking as well (and yes, it could choose itself). Finally, it was replaced by exert.

Rulings

 * If you declare exactly one creature as an attacker, each exalted ability on each permanent you control (including, perhaps, the attacking creature itself) will trigger. The bonuses are given to the attacking creature, not to the permanent with exalted. Ultimately, the attacking creature will wind up with +1/+1 for each of your exalted abilities.
 * Some cards with exalted abilities have other abilities that also trigger when a creature you control attacks alone. Each time a creature you control attacks alone, both the exalted ability and the other ability will trigger.
 * If you attack with multiple creatures, but then all but one are removed from combat, your exalted abilities won't trigger.
 * Some effects put creatures onto the battlefield attacking. Since those creatures were never declared as attackers, they're ignored by exalted abilities. They won't cause exalted abilities to trigger. If any exalted abilities have already triggered (because exactly one creature was declared as an attacker), those abilities will resolve as normal even though there may now be multiple attackers.
 * Exalted abilities will resolve before blockers are declared.
 * Exalted bonuses last until end of turn. If an effect creates an additional combat phase during your turn, a creature that attacked alone during the first combat phase will still have its exalted bonuses in that new phase. If a creature attacks alone during the second combat phase, all your exalted abilities will trigger again.
 * In a Two-Headed Giant game, a creature "attacks alone" if it's the only creature declared as an attacker by your entire team. If you control that attacking creature, your exalted abilities will trigger but your teammate's exalted abilities won't.

Creature that grants Exalted

 * First Sliver's Chosen
 * Sublime Archangel

Plane card that grants Exalted

 * Bant (all creatures)

Trivia

 * Exalted was featured as rules card 1 of 5 in the Shards of Alara set.
 * Exalted Angel and Exalted Dragon don't have exalted.
 * Angelic Exaltation acts similarly as granting Exalted to all your creatures, but with fewer triggers. Sigil of Valor does also, for all but the equipped creature.
 * Alter of the Goyf acts similarly, pseudo-turning the attacking creature into a Lhurgoyf.