A fanlisting is simply an online list of fans of a subject (in this case for forte stollen) that is created by an individual and open for fans from around the world to join.
There are no costs, and the only requirements to join a fanlisting are your name and country. Fanlistings do not have to be large sites (although some are), they are just a place where you can sign up with other fans. TheFanlistings.org is the original (but not official) web directory for fanlistings, dedicated to uniting the fans.
Description from tfl.

forte stollen

Forte is one of the girls of the "Angel Unit". She's the oldest one (her age is 22 years old) and peraphs the most serious of the main characters of the show. She has an insane passion for weapons (guns mainly) and she oftenly acts in a sort ot masculine way, still she can always show she's a charming woman and she has a deep and feminine side she tries to hide with all her means. She has a bad temper but mainly because she finds difficult to get along well with the crazy partners she has in the Angel Unit. It seems she also loves to shoot Normad when she needs to relax or when he speaks too much (very oftenly too!). If you wish to know something more about her...well I suggest you to watch the anime or to read the manga, you won't be disappointed at all!