The Other Hardy Boys Series

current series

Starting in 2013, The Hardy Boys Adventures is a series of books, similar to the Nancy Drew Diaries, which replaced the Undercover Brothers Series.
Clue Books
The Clue Book series (starting 2016) is aimed at younger readers like the similar Nancy Drew Clue Book series.

past series

Be A Detective
The Be A Detective Mysteries (1984-1985) teams Nancy Drew & the Hardy Boys in a series of mysteries in which the reader controls the outcome of the story by choosing different options of advancing the plot. Carolyn Keene and Franklin W. Dixon are listed as co-authors and each book contains a forward by them.
The Casefile series (1987-1998) is aimed at early-to-mid teen readers and have more mature, espionage based themes, similar to the then-current Nancy Drew Files series.
Clues Brothers
The Clue Brothers series (1997-2000) aimed for younger readers like the similar Nancy Drew Notebooks series. These short, simple mysteries recounted the adventures of Frank and Joe's first years in Bayport. In addition to several new characters, most of the regulars from the original series also showed up.
The Digest series (1979-2005), published under various imprints of Simon & Schuster, picked up where the original Hardy Boys series ended. The stories and characters remained the same as in the original series.
Secret Files
From 2010 to 2015, Frank (age 8) and Joe Hardy (7) solved cases in this chapter book series for younger readers, similar to the then-current Nancy Drew Clue Crew books.
Super Mysteries
From 1988 to 1998, Nancy Drew and the Hardy Boys joined forces in this 36 volume series by Carolyn Keene published by Simon & Schuster under their Archway imprint.
Ultra Thrillers
In 1992, Tom Swift joined forces with the Hardy Boys in the two volume Ultra Thriller series. With both volumes having a science fiction themed plot, the series is closer to the then-current Tom Swift IV series than the then-current Casefiles series.
Undercover Brothers
Replacing the venerable Digests, this series (2005-2012) finds the Hardy Boys having been drafted by American Teens Against Crime (A.T.A.C.), a top-secret government agency, founded in part by their father. The Undercover Brothers Graphic Novels (2005-2012), the new Super Mystery series (2007-2012) and the New Case Files (2010-2011) will be found here.
Other Books
Here's where you'll find miscellaneous Hardy Boys books, such as activity books, coloring books and other odd editions.
Nancy Drew-Hardy Boys Comics
Starting in 2017, a new comic/graphic novel series.

Hardy Boys Case File 128 Unpublished Manuscript
I have a copy of the manuscript of the unpublished Case File #128, "Explosive Force"
with editor's comments but missing pages 90, 132-137, 149.
I'll make a copy for you for $50 postage included (to USA only).