I didn't want my Celtic game to be full of typical fantasy races like elves, dwarves and orcs. At the same time, making everyone play a standard human can be kind of boring and ignores the awesome racial abilities available in 4E. So I gave the players the advantages of both--some of the human racial traits, and additional traits from other races. Note that this list was written right after the PHB2 came out, so it doesn't include more recent racial abilities.
The only race available is human. The tribes of Tir Nan Og are remnants of sunken Atlantis, although they have mixed their blood with the many peoples of the continent. The Tribes are more concerned with cultural heritage than blood ancestry, so folk of all appearances are found among their ranks.
Humans get +2 to two ability scores, an extra feat and trained skill at first level, and one major and one minor trait off of the list:
Major Traits
Accuracy: You rarely miss. You can use the elf power Elven Accuracy as an encounter power.
Changeling: You can use the doppelganger power Change Shape as an encounter power.
Child of Darkness: You have a touch of dark fey blood, or perhaps you were born during an eclipse. Once per encounter you can use the drow power Cloud of Darkness or Darkfire.
Dilettante: At 1st level, you choose an at-will power from a class different from yours. You can use that power as an encounter power.
Furious Assault: You can use the half-orc power Furious Assault as an encounter power.
Hide of Bronze: You can use the goliath power Stone’s Endurance as an encounter power.
Memory of a Another Lifetime: You have been reborn from death before. You can use the deva power Memory of a Thousand Lifetimes as an encounter power.
Otherworld Step: You can step briefly into the Otherworld and step out in a different space. You can use the eladrin power Fey Step as an encounter power.
Second Chance: You can use the halfling power Second Chance as an encounter power.
Shake It Off: You can use the hobgoblin power Hobgoblin Resiliency as an encounter power.
Spiral Energy Surge: Your body is marked with a scar or birthmark similar to a weirdstone mark, and you can channel Earth Power into a violent blast. You can use the dragonborn power Dragon Breath as an encounter power.
Training: You know an extra at-will power from your class.
Minor Traits
Berserker Resilience: The first time you are bloodied during an encounter, you gain 5 temporary hit points. (10 hp at 11th level, 15 hp at 21st level)
Bear’s Toughness: You can use your second wind as a minor action.
Blood Fury: When you’re bloodied, you gain a +1 bonus to attack rolls.
Bloodhunt: You gain a +1 bonus to attack rolls against bloodied foes.
Educated: You have an extra trained skill.
Eidetic Memory: When you make any knowledge check, roll twice and take the best result. This cannot be used when making a skill check for a ritual.
Infernal Wrath: You can use the tiefling power Infernal Wrath as an encounter power.
Mighty Build: Your oversized body allows you to use a two-handed weapon in one hand.
Powerful Athlete: When you make an Athletics check to jump or climb, roll twice and take the best result.
Self-Reliant: +1 to Fortitude, Reflex and Will Defenses.
Quick Step: Your base speed is 7 instead of 6.
Stand Your Ground: When an effect forces you to move—through a push, a pull, or a slide—you can move 1 square less than the effect states. Also, if you are knocked prone you can make an immediate saving throw to avoid falling prone.
Untiring: Add your Constitution modifier to your healing surge value.
Wild Step: You ignore difficult terrain when shifting.