Dragon mag (also in the old crystalkeep classes pdf) has the "Focus Caster" ACF. You choose one school of magic, but it does not require you to be a specialist of that school -- you could even be a specialist in a completely different school! The school determines what type of item your focus must be (Evocation uses a weapon, transmutation a tool or musical instrument, etc...) and generally the benefits apply when casting spells of that school.
IMO, unlike most Familiar replacements, which are either grossly overpowered (Abrupt Jaunt) or underpowered (most of the other ones), the Focus Caster ones, overall, are pretty well designed. They all give a benefit at Wizard 1, 7, and 15, so they still punish you for prestige classing out, but you'll at least get one or two benefits. For example, evocation focus caster at 1 gives you +1 damage on all evocation spells; at level 7 lets you ignore the first 5 points of energy resistance; and at level 15 lets you ignore energy immunity 1/day. Transmutation Focus Caster at 1 lets you pick an additional target for any targeted Transmutation spell you cast (both helpful and harmful), but at half the normal duration if applicable. I forget what the 7 and 15 abilities are, one of them makes the extra target get full duration, in any case, I think the Transmutation FC is a great ability. Enlarge two allies at once, give two people Fly, Baleful Polymorph two foes into squirrels!
