说明：  1,在服务器端如何维护已经登录的用户列表； 2,反向通讯，通过服务器端给客户端发送文件； 3,实现客户端与服务器端的Chat聊天功能（稍加改动可转化为C->S->C的聊天程序） 4,如何使用IdTCPServer和IdTCPClient控件 5,初步实现线程命令方式，在传送文件的时候不会让服务器端停止响应 本Demo通过D7+Indy Snapshot 版本编译通过，请不要使用任何Delphi自带的Indy编译（包括BDS2006， 因为这些Delphi自带的版本都有Bug）
(1, the server side how to maintain a list of users already logged on 2, reverse communication, through the server to the client to send the file 3, to achieve client and server-side Chat Chat (little change can be converted to C-> S-> C of the chat program) 4, how to use IdTCPServer and IdTCPClient control 5, a preliminary approach to achieve thread command, when sending the file will not allow the server to stop responding via D7+ Indy Snapshot Demo version to compile, please do not use any Delphi Indy native compilation (including BDS2006, as they bring their own versions of Delphi have Bug))