Some free online Mario games are "Test Your Mario Memory," "Test Your Mario Knowledge," "Mario's Game Gallery" and "Donkey Kong." These games are available on the official Nintendo and Internet Archive websites.
"Test Your Mario Memory" is similar to the classic "Memory" board game, except the cards feature characters from Mario games. "Test Your Mario Knowledge" is a trivia game based on Mario and other characters in the franchise.
The Internet Archive features a couple of classic MS-DOS Mario games. In "Mario's Game Gallery," players choose between playing checkers and other classic games with Mario. "Donkey Kong" is also available on the website and is the first game to feature the Mario character.