Fahrenheit / Celsius / Kelvin / Rankine Choose-your-own-adventure game Multiplication table Figures - with specified text or with * * *** ***** ******* ********* reverse a text string check if a string is a palindrome sort by swaps (selection sort) primes Pascal's Triangle, Sierpinski numbers to text (e.g. "four thousand two hundred sixteen dollars and fifteen cents") gambling games calculations - Fibonacci numbers complete graph edges pi (Monte Carlo, sequences) Caesar cipher simple substitution cipher day of the week for any date stock symbol lookup program (using Quote.py by Jon Corbet) word ladders anagram dictionary concordance generator or word frequency counter spell checker haiku generator or detector (like Don Marti's program to find haiku in technical documentation) text adventure game cellular automata, Game of Life maze navigation icon editor diary editor 15 puzzle animal game one-time pad crypto ciphersaber CGI script networked chat file transfer or e-mail networked game (plus trust issues) book catalogue or other database GUIs graphics - fractals graphs pretty patterns file browser toy language OOP or procedural stack OOP or procedural tree OOP deck of cards OOP polynomials OOP simulation of some real-life event Quine program generate HTML some kind of HTTP user agent examples that come with Python