To be found
To keep things in line with the low-magic setting, I've limited spellcasting, and set the level cap at 6 (using the E6 variant of the d20 system.)
Species
Mice have +1 to all skills, and +1 to any one stat.
Otters have +1 Dex, +1 Str, and receive a +4 to all checks to hold their breath
Squirrels have +2 Dex, and +4 to all climbing checks
Moles have +1 Str, +1 Mind, and can burrow at their normal speed
Badgers have +4 Str, -2 Dex, and free proficiency in their trademark weapon
Hedgehogs have +1 Str, +1 to one skill, and +1 Natural Armor
Classes
Warriors can wear any kind of armour and use shields. They are proficient in simple and martial ranged and melee weapons, and one exotic weapon. They have a +3 bonus to Physical and add +1 to all attack and damage rolls. This increases by +1 at 5th level.
Scoundrels can use light armour. They are proficient in all simple and martial light and ranged weapons. They have a +3 bonus to Subterfuge. If they successfully Sneak (usually sub+DEX, but depends on situation) up on a foe they can add their Subterfuge skill rank to the damage of their first attack.
Seers do not wear armor. They are proficient in simple weapons. They have a +2 bonus to Communication, and a +3 bonus to Knowledge. Seers can cast Illusionist spells as an Illusionist of half their level.
Scouts can use light or medium armor and can use shields. They are proficient in all simple weapons, and ranged martial weapons. They are +1 to hit and damage with ranged weapons and only incur a -1 to hit penalty when fighting with 2 weapons. They have a +3 bonus to Survival.
Monks do not wear armor. They are proficient in simple weapons. Monks have a +3 bonus to Communication, and a +2 bonus to Knowledge. A monk can heal up to 5 HP a day by applying a poultice or other woodland remedy.
Prestige Levels
A Prestige Level is a level that a character has to qualify for by deeds, quests, or renown. It replaces the normal sixth level with additional benefits (weapon specialization, Bloodwrath, followers, etc.)
Details are still being worked out, but possible options include Badger Lord of Salamandastron, Warrior of Redwall, Skipper of Otters, Abbot of Redwall, etc.