Sometimes it is optimal to group keywords into tight groups. For example when paying for pay per click ads you can group similar keywords into a group and show the same ad for those keywords.
This tool will help you accomplish that with only a few clicks.

Load in your keywords and click the "Group Keywords" button. For large list of keywords this may take a a few seconds.

You will get back a tree list of groups.

You can the select the groups you would like to copy, right-click on one of them and click Copy.

Look at the screenshot below to see this tool in action: