Take 3: Based on B/X D&D stats.
Yes, this is Take 3. I wrote Take 1 while coming off pain killers and it was just god awful. It was ugly, inelegant, and way too complicated. I have scratched it and put this in it's place:
-Elf: +1 Dex, -1 Con. Elves have low-light vision.
-Dwarf: +1 Con, -1 Cha. Dwarves have thermographic vision. Dwarves also get a +2 to all saving throws vs. poison or disease.
-Ork: +1 Str, +1 Con, -2 Cha. Orks have thermographic vision.
-Troll: +2 Str, +2 Con, -1 Int, -1 Wis, -1 Dex, -2 Cha. Trolls have thermographic vison. Trolls do 1d4 with their unarmed attacks instead of 1d2. Trolls have a natural AC of 7. (Assuming descending 9 system) Trolls roll a hit die of one type higher than that of their character class. (So if the Street Samurai class rolls a d8 for hit points, a troll samurai is going to roll d10s, while a troll mage rolls d6s, etc._
Take 2: The SWN Version
These use Stars Without Number as a base. In SWN, some alien races get a bonus to a score's modifier, rather than the score itself. For instance, a troll with Strength 10 (normally a 0 modifier) has +2 modifier, making a troll with Strength 10 the equivalent to a human with Strength 18. On the other hand, a troll with Strength 15 (a +1 modifier) has a total modifier of +3; stronger than any human could ever hope to be. (Without cybernetics or other enhancements, that is...)
Human: No modifiers
Elf: +1 Dex mod, -1 Con mod, Low-Light Vision
Dwarf: +1 Con mod, +1 Physical Effect save vs. disease/poison, Thermographic Vision
Ork: +1 Str mod, +1 Con mod, -2 Cha mod. Thermographic vision.
Troll: +2 Str mod, +1 Con mod, -1 Int mod, -1 Wis mod, -2 Cha mod. Thermographic vision, Natural AC 7