When Benjamin Franklin died in 1790, he willed the cities of Boston and Philadelphia $4,400 each, but with the stipulation that the money could not be spent for 200 years. By 1990 Boston’s trust was worth over $5 million.
The money was in trusts that were to lend money to budding tradesmen to help them set up their shops early in life. Upon the first 100 year anniversary, a certain percentage was released to the city for setting up trade schools. Upon the 200 year anniversary, the remaining funds were released in whole to the city treasuries.
Franklin set up detailed instructions as to how the loans and releases were to work, and calculated estimated values. Both trusts ended up coming up shorter than Franklin had estimated (usually attributed to less than expected repay percentages on the loans), but still managed to do a world of good for each city. (Source)