10 Ways You Can Play Fourth Edition Now (Thanks to Chris Nightwing for an earlier version; some of this is conjecture):
1) Give 1st level characters triple hit points (but apply Con only once). At the end of an encounter, a character who is unconscious stabilizes at -1 hit points. Conscious creatures who are below half their full hit point total heal to 1/2 their full. Creatures who are above half heal to full.
2) Saving throws are replaced by Fortitude, Reflex, and Will defense, which start at 10 + your level. Classes with a good progression of a given save get +2 to the associated defense. When multiclassing, use the best bonus for each defense; they don't stack. Whenever an ability would normally call for a saving throw, the initiator rolls d20+their level+associated ability score (Int for Wizards, for instance) against the appropriate defense.
3) Characters also gain a +1 dodge bonus to AC per level.
4) Remove metamagic and item creation feats. Any character can create magic items now if they have the appropriate spells and caster level. However, magic items are much less necessary. Half the recommended character wealth at each level. Remove all items that grant bonuses to AC and saves, other than armor and shields. Weapon and armor enhancement bonuses do not go above +1.
5) Replace sorcerers and wizards with warlocks, but let warlocks acquire spellbooks. Each day they can cast one spell per level, to a maximum spell level of half their class level rounded up. However, these spells are rituals, and their casting time is extended by ten minutes.
6) Every character's base attack bonus is +1 per two levels (as a wizard), but classes with average progression get a +1 at 1st level, and classes with good progression get +2 at 1st level. As with saves, when multiclassing just use the best bonus. Also, there are no iterative attacks. Characters get a bonus to weapon damage equal to their base attack bonus.
7) Let characters with special ablities such as Smite or Rage use them once per encounter instead of limiting them per day. Encourage fighters to take martial feats to gain maneuvers and stances from the Book of Nine Swords.
8) Combine skills, for instance Hide/Move Silently -> Stealth, Spot/Listen/Search/Sense Motive -> Perception. Remove synergy bonuses. Otherwise keep skill points, ranks and standard DCs for ease of play.
9) Enhance the changes made by playing a particular race as character level increases. Grant abilities from the racial paragon classes of Unearthed Arcana every 5 levels.
10) The Marshal is a base class, but it gains a bonus feat at 1st level and every even level, which can be used to learn martial maneuvers and stances of the White Raven style.
