While the majority of clients tend to leave property to family members in their estate plans, there are certainly cases when money is left to friends. In addition, it is not uncommon for a friend to be named in a fiduciary capacity, as either an executor or trustee.
Friends can make good fiduciaries if they can act impartially, as they do not always bring same the emotional baggage as a family member. However, family members are often eager to challenge estate plans which favor friends, and clients should consider adding a no-contest clause (also known as an in terrorem clause) where appropriate to dissuade a challenge.
Sara Murphy provides some insights to including friends in your estate plan in the New York Times:
How to Leave Your Friends an Inheritance After Your Death – The New York Times (nytimes.com)