What is it?
SAP.net connector allows .net to communicate with SAP via the SAP Business Application Progamming Interface's (BAPI's) using VB or C#.
Where do I get it?
Microsoft and SAP integation is possible via the SAP.connector which is available to SAP customers via their development network (SDN).
How does it work?
The SAP.connector has been around for a while now and can be used to generate proxy classes which can be used within your Microsoft .net project.
The SAP.net connector was released prior to Version 2.0 of .net and worked well with Visual studio 2003 (.net version 1.1) IDE to produce the proxy classes. However since the subsequent releases of Microsoft VS, there have been no further releases of the SAP.net connector and some work around is required to use the proxy classes within the most recent version of the Microsoft Visual Studio offerings.
Seamless Integration
Nevertheless SAP.net connector has made integration of Microsoft .net solutions with SAP seamless. In fact anything you can achieve by executing SAP BAPI's (Business Application Programming Interface's) you can do from .net.
Two Skillsets
Two skill sets need to work together here to make the whole thing work though. You would need a ABAP developer who could package the custom logic and .net developer who can work with web services. Yes, the BAPI that is written in SAP can be exposed as a web service proxy, which the .net developer can use.
BAPI and MSQL Stored Procedure Analogy
In Microsoft world you could think of the BAPI's as stored procedures with input and output parameters. However these parameters as well as standard types like a string, integers can also be a .net class or even a collections of classes. In the SAP world the classes are known as structures. A .net developer can then interact with these classes (structures) before invoking the BAPI.