Racial Paragon Class
Remember when Elf, Dwarf, ect. were classes? Third Edition version of Unearthed Arcana introduced an idea in that spirit in Racial Paragon Classes. Like a base class, a Racial Paragon Class can be taken at first level, and like a Prestige Class is less than 20 levels long (only 3), has requirements (count as the right race and no levels in another racial paragon class) and doesn’t cause multiclass XP penalties (not that anybody uses those rules). They’re implied to ignore the mutliclass restrictions class like Monk and Paladin have, but not clearly stated (and again, it’s not like anyone uses those rules). All share the feature of gaining a +2 to an ability score (typically for a fixed ability) at third level. Individually most are not really notable since they don’t give any abilities or enhance useful ones, to the point most could be seen as Tier 6 on their own.
Human Paragon gives the ability to pick any ten skills as a class skills (like an Expert, but with only 4 skill points instead of 6), and the ability to select one of those skill to always be a class skill. At level two it gets any feat as a bonus feat, which is really useful for many builds, and an increase in any spellcasting classes it has. At level three it gains another effective casting level and an ability score boost. A one or two level dip into human paragon helps a lot of weirder builds function.
Half-Elf Paragon gets a bonus feat at first level alongside a boost to search and spot, and the option to take levels in Human Paragon or Elf Paragon. The feat is very nice, though since half-elfs in 3E have basicly no racial features besides counting as an elf without a con penalty, the question of "why not just play a human" comes to mind. Nobody is going to take further levels (except maybe theorycraft build trying to get a single stat as high as possible for its own sake) since the rest it gets are trash.
Half-Drow Paragon gets casting advancement at its first level (but only for cleric and wizard), on-top of bard proficiency and an extra use of their SLAs. This makes it an option for a Half-Drow Cleric/Wizard that needs a martial weapon to qualify for a prestige class, and maybe a cleric that’s willing take a BAB to use longswords. The real most notable thing about it is putting a lot of the drow fluff under the Open Gaming License.
Half-Orc Paragon is easily the most powerful of the group on its own, but least useful for builds. This is because it’s a variant Barbarian. Seriously, it’s on the Barbarian chassis and has class features of a bonus to intimidate, a Barbarian’s rage, and a boost to Strength as its class features. Curiously literate and capable of being lawful unlike a true barbarian.
Tiefling Paragon is notable solely because it’s a class with all good saves, so one level will increase all saves by 2, and two will increase all by 3. One level will also increase one of your natural resistances by 5, which at least synergies with good saves (pick fire, since its the most common and it puts you over the threshold of being immune to mundane fire). Two will give an extra use of your SLA and boost your racial skill increases.
The rest of the options are all so terrible as to be not worth a second look.