What is the relationship between wvdial, pon and chat?

I've checked their man pages, but I'm still confused. I just know they are all related to ppp connections. I'm surprised that when I googled "pon wvdial relationship", I get no useful results, so I ask this question here. Who can tell me the role of these three tools? I still feel they do the same thing... and... I find that a new tool - pon.wvdial has come out, and what is it? I'm really confused with these tools...