There are some ways to reach the title issue:

1. webservice

2. Remoting

3. ipc(obviously, it is one of Remoting)

4. dataBase

5. SendMessage(windows API)

6. MSMQ(Microsoft Message Queuing)

       For my Solution, I just wanna communicate between two separate applications (winform) in a machine. Also, both of the applications are using .net to develop. So I chose "ipc" and"SendMessage". I am not clear how about the MSMQ :)

       As to Webservice , it is suit for multi-language, multi-platform

       And Remoting is better used for network communicate in .net

       The database just can share the data, but can't send message from one application to another.