Microlite74. Microlite74 was, naturally, designed to "feel like" 0e style D&D, although utilizing a minimalist interpretation of d20. I don't know that the differences are really all that major between Microlite74 and other Microlite fantasy games (in fact, I'd argue that they are not) but I was, at least, not terribly thrilled that my magic system for DARK•HERITAGE felt like the magic system for D&D, which is mostly did.
So, I've tweaked it ever so slightly.
First off, it's not my intention that the game should ever be played beyond 10th level. Because of this, I've only made available up to 5th level spells normally. As in the rest of the microlite family, there isn't any "fire and forget" or spell-slot type mechanism; it costs you hit points (that can't be healed magically) to cast spells, which naturally limit your ability to continue casting ad nauseum but which feels much more "naturalistic" than spell slots, which always felt really arbitrary and weird. In addition to not having spells over 5th level, I also trimmed the spell list just a bit for spells that just didn't feel right for my game.
In reviews (and after a glance at the rules I agree that this is most likely true), the sorcerer is probably too powerful. Lacking many of the "lows" of typical d20 magic-using classes, like low BAB or low hit points, but still having access to potent spells with the relatively "cheap" cost of taking a few points of hit point damage when casting them, this was neither balanced, nor did it fit with the tone of my setting.
Also, the spells were so recognizably D&D spells, that they would never feel like anything other than D&D anyway.
So... a few things needed fixing. First off, casting spells also comes with a risk of taking damage to your MND score. This approximates the sanity cost that spellcasters would incur in a game like d20 Call of Cthulhu--right up my alley. Secondly, I only took the magic-user class and the arcane spell list; there's no such thing as divine magic or clerics (either with another name or not) in my world. Thirdly, if you roll a natural 1 on your "save" to avoid taking the MND damage, you attract the attention of 1d3 hounds of Tindalos with your bumbling meddling with the forces that separate the Realms (by metaphysical theory, magic is taking energy from one realm, or from the space between realms, and using that energy to create an effect that is out of whack with natural law within the realm in which you cast it.) Casting a spell, taking both hit point and MND damage and then having hounds of Tindalos show up to attack you makes using magic a risky affair--again, exactly in line with the tone of my setting in which the supernatural is fundamentally an unnatural and dangerous thing.
Then, I also used the ritual magic rules, which are in one of the versions of Microlite74 anyway, to bring some spells back. I have a truncated list of higher level spells which can only be cast as rituals. You can also cast any spell on the spell list, even if it's not in your repertoire, assuming you have a copy of the ritual requirements, as a ritual. Rituals are even more dangerous (in many ways) than regular spells, and they take a lot longer. You can, however, spread the risk around and mitigate it by casting it as a coven, or with a partner or two.
Finally, I renamed all of the spells, even though I did very little to change their effects. Even though the game rules may be the same, casting magic missile feels like D&D, while casting withering of the Haunter does not.