On the Command and Command Block page on the Minecraft Wiki, there are lists and tables describing the
- commandBlockOutput - Whether command blocks should notify admins when they perform commands.
- doFireTick - Whether fire should spread.
- doMobLoot - Whether mobs should drop items.
- doMobSpawning - Whether mobs should naturally spawn.
- doTileDrops - Whether blocks should have drops.
- keepInventory - Whether the player should keep items in their inventory if they die.
- mobGriefing - Whether creepers, endermen, ghasts, and withers should be able to change blocks.
- doDaylightCycle - Toggles the day-night cycle (the sun stops moving and stays where it is) (added in 1.6.1)
- naturalRegeneration - Toggles natural health regeneration (Ibid)
Source: Minecraft Wiki
In Minecraft, you can type
/gamerule Tab and keep pressing Tab to iterate through all (if no hidden ones) available game rules. When the rule you want appears, just press Space and input either
I believe the rule name itself is already quite self-explanatory, if not you can refer to the list above or the Minecraft Wiki or try them yourself.