|Editing:||Please feel free to edit constructively!|
Third edition D&D is infamous for it's daily uses of abilities while fourth edition has split uses into "at-will", "encounter" and "daily." Where many 3rd edition fans may not like 4th edition as a whole, this aspect is very useful to characters who have many abilities such as spellcasters.
To do this merely cut the daily uses of an ability in half (round down) and that is the number of times per encounter the character can use it. If a character can use an ability more than four times per encounter, it becomes an at-will ability.
For spellcasters a single "spell level" is considered an ability. So a 4th-level Wizard that can cast four 1st-level spells per day would instead be able to cast up to two 1st-level spells per encounter.
Metagame analysis: For healing spells and creation spells this creates a problem. To fix this, require 10 minutes of rest to renew encounter uses.