I'm generally such an isolated throwback that I hadn't even heard of 'niche protection' until just a few weeks ago. In spite of not having heard the damned term, the idea that each class in a RPG should have its own thing was apparent during the development of Heroes Against Darkness.
One aspect of this division of capabilities and specialties is the separation of the magic into the five main magi classes:
• Warlocks who specialize in physical manifestations and offensive spells
• Healers with their specialization in physiological magic that heals, enhances or weakens
• Canonates who enforce the will of their divine god to buff allies, bless areas and attack enemies
• Necromancers who can raise and control undead, drain health and anima from enemies
• Mystics who are masters of control and influence, to help and hinder
During playtesting of Heroes Against Darkness, one of the players would constantly ask for utility spells, like in D&D. I resisted his requests because the utility spells that he was asking for are the very spells that break the niches, they are the spells that allow wizards/sorcerers/clerics to become the Swiss Army knife classes who can do anything, anytime. The main culprits in D&D are the spells that directly replace the class features of other classes, such as Knock, Invisibility, and the like.
Knock has the unfortunate privilege of making rogues/thieves just about useless. Once you've got Knock, there's no locked door or chest that can't be opened by a night's rest and a quick spell. If that wasn't bad enough, a sneaky rogue can be replaced with Invisibility as well.
In Heroes Against Darkness these sorts of spells don't have absolute effects, rather they offer enhancements to the target's ability tests, making these spells most effective when cast on a character that is already good at the activity, rather than allowing the spell to be cast on any character. Even spells like Charm and Divine respectively enhance the character's Charisma and Perception, rather than having absolute effects. The final advantage of the enhancement approach means that the spells effects are still relative to the state or difficulty of the target, so a Charisma or Perception enhancement takes into account the underlying difficulty of the activity that is being undertaken.
So, if you're after spells that allow magi to replicate the features of other classes, then these are not the rules you're looking for.
Check out Heroes Against Darkness over at the downloads page: Heroes Against Darkness - Game Rules.