whats the difference between Adobe AEM Forms Designer 6.5 and Adobe AEM Desktop 2.1.5.0

@user96 - The two products are used for different purposes.

AEM Desktop App - Using the Adobe Experience Manager desktop app, the assets within Experience Manager are easily available on your local desktop and can be used in any native desktop applications. Assets can be previewed, opened in native desktop applications, revealed in Mac Finder or Windows Explorer for placing in other documents, and changed locally – the changes are saved back to Experience Manager when you upload and a new version is created in the repository.

Reference - https://experienceleague.adobe.com/docs/experience-manager-desktop-app/using/introduction.html?lang=en

AEM Forms Designer -

Designer is a point-and-click graphical form design tool that simplifies the creation of forms. Form recipients can fill a form online, submit the data, and print it, or print and fill the form by hand. You can design a form, define its logic, and modify it to match paper counterparts or to meet strict legislative requirements. Form developers can use Designer to create applications that generate dynamic, data-driven documents and produce customized business documents for print, web, or archival. 

Reference - https://www.adobe.com/accessibility/compliance/aem-forms-designer-6-5-acr.html

Hope this helps!