First off, congratulations for wanting to contribute to this project!
If you would like to contribute to a tool which hasn't been started yet please do, make sure to put in a pull request when you get the simpliest prototype possible so that no one else starts on it!
If you would like to contribute to a tool which is in the progress of being developed then you can make your changes along with a pull request, it will be reviewed the next time I see it.
If you would like to contribute to a tool which has already been written then make your changes, unless it is a bug, after they're reviewed it will be in an "in progress change" and the next time a bug or big change happens to it your changes will be pushed.