Some add-ins are built in to Excel, such as Solver and the Analysis ToolPak. Other add-ins are available from the Download Center and must first be downloaded and installed. Finally, there are add-ins that are created by third parties, such as a programmer in your organization or a software solution provider. Knowledge And Politics. These can be Component Object Model (COM) add-ins, Visual Basic for Applications (VBA) add-ins, and DLL add-ins. These add-ins must also be installed to use them. Most add-ins can be categorized into three different types: • Excel add-ins These typically include Excel add-in (.xlam), Excel 97-2003 add-in (.xla), or DLL add-in (. Heyl Scholarship Program. xll) files or they are automation add-ins.