Catalogs and inventories can be created in many formats, using many different technologies. You may recall that library catalogs were once cabinets full of carefully organized printed index cards. Today, catalogs can take forms ranging from simple but organized text documents, to spreadsheets, to more complex databases.
Some easily accessible tools to make inventories or flat/single-entity catalogs:
Some easily accessible tools to make catalog databases:
These tools can provide the technological basis for your catalog, but you will still need to build it according to your own structures and rules, and enter the data to create the catalog records.