itch.io

Very cool! I can look into creating a theming guide and template, but for sounds and add-ons there's currently no way for me to enable other people to be able to make/add them to the program. 

Hi meowcifer! I've created a custom theme template and documentation for it, and put it on github. Give it a try if you like. You'll be a bit of a guinea pig here as it's a work in progress and you'll be one of the first people to use it https://github.com/beastly-eve/stimuwrite-theme-template