Facebook has launched the ability to let users chat within applications on Facebook. This keeps applications within the social network even more social.

If a developer uses the new fb:chat-invite FBML tag, they can display a list of users’ online friends and let them invite their friends to chat. Developers can also give users the freedom to choose which friends they want to appear in their chat lists within the apps.

Gmail chat has come to iGoogle. This means users will be able to chat with their friends and associates without leaving the comfort of their Google homepage.

The feature is not a gadget like most of your iGoogle features. The chat feature comes in the form of a sidebar and resides below the left-hand navigation menu.

Yahoo announced that it now offers an SMS chat feature in its classic version of Yahoo Mail, something Gmail has been offering for several months, and Yahoo has been doing in its newer version since 2007.

Google has offered SMS in its chat since October, and Chat in general for quite some time. They have also launched voice and video chat recently.

Google has added a new feature to Gmail, which allows users to watch videos within their chat windows. This eliminates the need to leave your Gmail window when someone sends you one.

Instant messaging and group chat provider Meebo is now allowing users to communicate with each other through both MySpace and Facebook IDs as well as all the other ones previously supported, like AIM, Yahoo, Google, MSN, Jabber, ICQ, etc.

We’re just trying it out for cell phones in the United States right now, but you can send texts to your friends with US phone numbers from anywhere in the world.