RakNet drops licensing fees
In case anyone here was looking for a network API, it might interest you that RakNet has dropped all licensing fees for all versions. Those wishing a grant of license for commercial products can apply from the site http://www.rakkarsoft.com . The GPL version is still available as well.
So this post doesn't seem like an advertisement, please feel free to look at the source in case you want to learn anything. It implements a vast array of features. They are all listed from the site.