OSR Eberron

Warforged for OD&D and Labyrinth Lord
They're not exactly as they appear in the Eberron setting, with a few more vulnerabilities.

Requirement: CON 9
Prime Requisite: CON
Hit Dice: 1d8
Maximum Level: 12
Experience Table: As Dwarf

Special Abilities:
Immune to most normal diseases, sleep, nausea, fatigue and exhaustion
Immune to many common poisons
No need to sleep, eat or rest
Unable to use items which must be eaten or drunk
Saves vs. poison as a dwarf
Cannot be healed by cure spells (not even half,) but can be repaired by a technician or mended by wizardry
Susceptible to poisons, diseases or other effects which affect living plants
Natural AC 7, armor modifications parallel normal forms of armor but are never encumbering

Shifter for OD&D and Labyrinth Lord
Requirements: DEX 9
Prime Requisite: STR and DEX
Hit Dice: 1d6
Maximum Level: 10
Experience Table: As Elf

Special Abilities:
Shifters are fighter/thieves in the same way that elves are fighter/magic-users. Saving throws are the most beneficial of either fighter or thief.

Each shifter has one of the six special traits as detailed in the Eberron campaign book, which is selected when a character is created and cannot be changed thereafter.

Gnome Artificer for OD&D and Labyrinth Lord
Requirements: DEX 9, INT 9
Prime Requisite: INT and DEX
Hit Dice: 1d4
Maximum Level: 8
Experience Table: As Magic-User

Player gnomes are artificers, as detailed in the Eberron campaign setting. Saves and attack table are as magic-users.

Infusions: An artificer is not a spellcaster, but he does have the ability to imbue items with magical infusions. They function just like spells and follow all the rules for spells. For example, an infusion can be dispelled, it will not function in an antimagic area, and an artificer fails if injured while imbuing an item with an infusion.
An artificer can imbue an item with any infusion he knows without preparing the infusion ahead of time.
It is possible for an artificer to learn infusions that are not on the normal artificer infusion list. These might include ancient infusions he finds in the ruins of Xen’drik or secret infusions known only to the members of certain guilds or organizations.
Like spellcasters, an artificer can use only a certain number of infusions of a particular level per day. His base daily infusion allotment is given on the accompanying table. In addition, he receives extra infusions per day if he has a sufficiently high Intelligence score, in the same way a magic-user gains extra spells.
An artificer’s infusions can only be imbued into an item or a construct (including warforged.) He can not, for example, simply imbue an ally with bull’s strength. He must instead imbue that ability into an item his ally is wearing. The item then functions as a belt of giant strength for the duration of the infusion. He can, however, imbue bull’s strength directly on a construct or a living construct, and infusions such as repair light damage and iron construct function only when imbued on such characters.
Many infusions have long casting times, often 1 minute or more, and the artificer must hold the item in his own hands.
An artificer can craft alchemical items as though he were a spellcaster.
An artificer cannot automatically use a spell trigger or spell completion item if the equivalent spell appears on his infusion list.
Each day, an artificer must focus his mind on his infusions. He needs 8 hours of rest. Without such a period of time to refresh himself, the character does not regain the infusion slots he used up the day before.
Artificer Knowledge: An artificer can detect whether a specific item has a magical aura. The artificer must hold and examine the object for at least 1 minute. A roll of 1 or 2 on a six sided die determines that the object has magical qualities, if it has any, but does not reveal the specific powers of the item.

Mechanic: An artificer can find and remove traps, and pick locks equal to a Thief of the same level, improving over time in the same way a thief does.

Craft Homunculus: At 4th level, an artificer can create a homunculus. He must emulate the spell requirements (arcane eye, mending, and mirror image) as normal for making a magic item, and he must pay all the usual gold costs. An artificer can also upgrade an existing homunculus that he owns, adding 1 Hit Die at a cost of 2,000 gp.
If an artificer gives his homunculus more than 6 Hit Dice, it becomes a Small creature and advances as described in the Monster Manual (+4 Str, –2 Dex, damage increases to 1d6).
An artificer’s homunculus can have as many Hit Dice as its master’s Hit Dice minus 2. No matter how many Hit Dice it has, a homunculus never grows larger than Small.

Number of infusions per day is as the table in the Eberron setting book. Available infusions are also as detailed in the setting.

Action Points
I feel this concept is important to the spirit of the setting, but to help it fit in with Labyrinth Lord I've made it more rare, while at the same time more consequential. Many things in old-school gaming are more concentrated. Spells are potentially more far-reaching and influential, yet they are fewer in number and further between uses. Combat doesn't occur as often, but when it does it's generally far more deadly.

Each character starts play with one action point. They receive another point every time they make a level, which may take quite a while. They also receive a point for achieving an outstanding success in completing an adventure or major goal. Did they go the extra mile and root out & defeat the hidden horror? Action point! Each action point is permanently gone when spent.

These points can be used to gain a dragonmark, or to upgrade an existing one. They can also be used to prevent death at zero hit points, lapsing into unconsciousness instead. Another use would be changing a failed die roll to a best-possible success. Since they are far more rare than the action points detailed in the campaign setting books, they don't just allow for a re-roll of a missed attack, for example, but rather would change a missed attack directly into a natural 20.