Lol I spent like 3 hours once making one. It was called BM, would check if the other person was using BM, saved all text into logs, saved your info in .idx's and allowed you to do autor responses (away messages). I gave one to my friend, on my network) and started having a conversation.
I made it into an EXE for my friend though because I didn't want him editting my code. Saved all the files into onto C:.