ACDSee Photo Studio is described as 'View, organize, and edit digital photos with support for 700+ RAW file types, advanced filtering, metadata integration, sharing options, and workflow improvements' and is a very popular Photo Manager in the photos & graphics category. There are more than 100 alternatives to ACDSee Photo Studio for a variety of platforms, including Windows, Mac, Linux, iPhone and iPad apps. The best ACDSee Photo Studio alternative is IrfanView. It's not free, so if you're looking for a free alternative, you could try IrfanView or XnView MP. Other great apps like ACDSee Photo Studio are Ente Photos, darktable, digiKam and RapidRAW.
ACDSee as a suite is so much more, but it is difficult to NOT compare one of the most popular "viewers" of all time to IrfanView. It would be wrong imo to not show those looking for an alternative VIEWER to ACDSee, IrfanView.