There are many different types of Qigong systems with different goals. There are
There are many more such types and each in turn has a large number of different variations. One analogy would be to think of Qi as music and the different types of Qigong as different musical instruments. The subject matter is the same but the way it is approached can vary. The Internal Martial Arts themselves are a type of Qigong.
A common thread in all these practices is the emphasis on using Mind. Most exercises are done with a great deal of (relaxed) concentration and very little of physical movement. But movement is present all the time - even when the practitioner seems perfectly still.
Recently, there has been quite a lot of research done on the health benefits of Taijiquan. Qigong research is just starting but the first indications are that (unsurprisingly) the benefits are similar.