Chess - Chess.com is a simple chess site that allows for computer play and daily puzzles for free. Some content may require creating an account.
Mancala - One of the oldest known games, Mancala is a simple, quick game if you need a little break. Fun for people of all ages!
Sporcle - Sporcle is an online trivia website with quizzes in a wide range of subjects.
2048 - Taking the iPhones by storm in 2014, this sliding-tile game is simple and addictive.
Internet Archive Software Library - Software Library hosts many of the 80s and 90s most beloved games, for a longer break, check out Oregon Trail and SimCity or try your hand at a quick game of Tetris, PacMan, or Bust-A-Move!