This is a (supposedly, with maintenance) complete list of templates on Rosetta Code.
As of this writing, most haven't been actively used in months. If you're looking for something to do, figure out if any of them are no longer needed. Otherwise some of them use poor formatting, and could use improvement. Finally, they should all be categorized according to the categories below. Be sure to include the category reference in <noinclude></noinclude> tags, so the pages the templates are used in don't get categorized in such a manner.
 Permanent templates
Most templates that should be placed permanently on a page denote categories like compilers, IDEs, programming languages, tasks, etc. Use Template:Task, Template:Puzzle, or Template:Language as an example of what a permanent template should look like.
Some templates, like Template:Header or Template:BoxImage, use special behaviors. Be careful about editing them; Here there be dragons. Some, like Header, depend on specific page placement. If you change the output of the template, you risk breaking something in how the page works. Practice in the Sandbox. In the case of Header specifically, you risk breaking the vast majority of pages on Rosetta Code. (But I trust you won't do that.)
 Temporary templates
Some templates are only supposed to be on a page briefly, like Template:Stub or Template:Broken. In order to speed their removal, they need to stand out. See the formatting for Stub or Broken for an idea of how to do this appropriately.
This category has the following 4 subcategories, out of 4 total.
Pages in category "RCTemplates"
The following 169 pages are in this category, out of 169 total.