I love old-school D&D (B/X, LL, Swords & Wizardry, OSE, etc) . . . except for the way that spellcasters have to memorize/pray for their spells each morning and magic is very predictable rather than mysterious and often dangerous. I've tried lots of variants and alternatives over the years: spell points, spell checks, spell mishaps, rituals, etc., gathering ideas from all kinds of sources, including the D&D books themselves, third-party supplements, other RPGs, and blogs and internet forums.

It seems that Eric Diaz has done that research, too, and synthesized the best ideas in one handy supplement. Alternate Magic is 32 pages in total, but the main alternatives to spell slots are covered in the first 11 pages, and they are what I'll be using the most. That's followed by descriptions of specific spells to go with some of the options (flexible/level-less spells, metamagic spells, cantrips, rituals), some alternative rules for clerics, and then descriptions of 5 new classes (Alternate Cleric, White Mage, Blood Mage, Chaos Sorcerer, and Pyromancer) that use some of the alternative systems. It ends with a couple pages on ideas for saving throws vs. spells and broad-stroke ideas for how characters find and learn new spells and for "living spells" that really follow different rules.

This is the most comprehensive yet concise resource I've found for someone who wants to spice up how magic works in their old-school games.