A few things

• Guitar tuner - Tune your guitar in your browser; no app necessary.
• FileViewer - View and analyze the inner structure of various file types.
• ELS code finder - Find ELS (equidistant letter sequences) in plaintext files.
• BinViewer - Visualize binary files as bitmap images.
• WikiPixel - Guess the celebrity.
• GeoQuest - Game of guessing the locations of obscure places.
• Did You Know - Fill in the blank of "did you know?" items from Wikipedia.