Because I answer a lot of questions under the Crystal Reports tags, I often see people misusing the tags. Below is a general description of what each is for:
SAP Crystal Reports - questions about general report design and how to use the Crystal Reports desktop software.
SAP Crystal Viewer - questions about the report viewer application that can be downloaded from SAP.
SAP Crystal Reports, version for Visual Studio - questions about coding with the .NET SDK.
SAP Crystal Reports, version for Eclipse - questions about coding with the Java SDK.
SAP Crystal Reports - SDK - questions about legacy SDKs, including the RDC.
SAP Crystal Server - questions about the Crystal Server software (questions about this software will often get a better response when also tagged with one of the SAP BusinessObjects tag as the underlying platform is the same with Crystal Server limited to just Crystal reports.)
NOTE: When running reports through SAP B1, you'll usually get a better response if you include the appropriate SAP Business One tag as well.