The fifth category are the mages. Mage are totally different heroes. They use different equipment and have different countermeasures when facing them. Their damage, rather than physical attack, use magic power: rather than physical defense, other need magic defense to be safe from their burst damage.
Best mages: Cecilion, Kagura, Valir.
The sixth and last category are the supports. They may also be mages, melee or long-ranged. Supports can help heroes farm faster or keep the enemy at bay while allied heroes farm. They can be quite useful in teamfight.