Microsoft Office provides you with quick access to "web-hosted add-ins" via the built-in Store by clicking Insert / Store which is found in the Add-ins group.
There are many more powerful add-ins available to you directly from legitimate third party software publishers of "client add-ins" (also referred to as application add-ins / VBA add-ins / COM add-ins). These are installed directly on your computer and integrate more tightly with the chosen Office application than the web-hosted add-ins, which is what makes them more powerful.
We've included a list of some of the PowerPoint client add-ins below and we encourage you to check them out as they provide functionality that you cannot find in the Office Add-ins Store.
Please feel free to share, copy and distribute this list.