If you mean HoneySelect with HS, then it's done with Unity version 5, although if you are serious about development and are looking similar engine, I would recommend Godot. There is new tutorial series just started for it in YouTube
HS mostly stands for "Honey Select" and is mostly used for VN images and videos, because of its Character Maker and Studio. With both you can made stills or videos without modeling everything by yourself. Make the characters you need, place them in the studio, build a scenario, add poses, animations etc. Because of the (great) mod community and the almost endless list of mods, the possibilities are endless. Same for Honey Select 2 (HS2) and Koikatsu (Sunshine). Last is used, if you like it more "anime style".