Several websites and application programs have been created over the years that can track Usenet newsgroups for keywords you are interested in, although there are less than there used to be.
These websites provide functionality to filter the Usenet feeds for specified keywords, and can therefore automatically find stories and posts of particular interest to you. Newsgroup postings containing those keywords can then be automatically retrieved and emailed to you no matter what newsgroup they were found in.
Unfortunately, there are no known indexes of these services. The last site known to provide Usenet filter services was Intellinews.com.
Various programs also provide Usenet filtering functionality through a standalone application that runs directly on your computer while connected to the Internet, although they are not covered here. Both web and application filtering services often provide a powerful range of advanced search capabilities, usually including boolean searching.