A basic knitalong is really nothing more than a group of people knitting one pattern or one "concept." The idea behind it, much like this forum-- is the sharing of knowledge and talents. There are a lot of knitalong groups out in cyberspace and real life-- some focus on charity knitting (there are lots of KALs (knitalong abbr.) for shelter pets, AIDS babies, etc.) and others focus on knitting for the fun of it. Some people join them to get access to a certain pattern, others want the community of being able to talk to another person about troubles with a common pattern, etc.
I think of a KAL as an afterschool group for knitters!