If like me you don't have the design skills to create sprites, characters and backgrounds, PowerPoint is a great place to start. The callouts make great buttons and power-ups in a game. They can also help you build a city, grow a forest or explore space.
To convert them into images you can use either SnagIt or Snipping Tool. Alternatively, take a screen capture (Alt+PrtScn) and use Paint to crop and resize.
Audacity is one of the best free audio tools I have found. You can very easily record a sound, then use the tools to turn it into an explosion, a mouse or a robot. The multi-track recording is great for creating a noisy crowd.
There are of course other free online tools to help you create sounds.
There are many free online tools that can help you create characters for your games:
To make your game really stand out from the crowd, consider the background of your game. You may have the skills to design this yourself, or you may like to explore these sites:
