A huge topic. Beginners should read Wikipedia for a general introduction then return here for more specific information:
Zhàn zhuāng, literally: “standing like a post”, is a training method often practiced by students of neijia (internal kung fu), such as Yiquan, Xing Yi Quan, Bagua Zhang and Taiji Quan. Zhan Zhuang is sometimes translated Standing-on-stake, Standing Qigong, Standing Like a Tree, Post-standing, Pile-standing, or Pylon Standing. It is commonly called a form of Qigong, despite the differences from other Qigong methods in Zhan zhuang's orientation.https://en.wikipedia.org/wiki/Zhan_zhuang
All of the Neijia arts *ex. Taijiquan, Xingyiquan and Baguazhang, etc.) agree that standing meditation leads to internal energy development, but they differ in the relative importance of that energy development and how the resulting energy is harnessed and used.
Yiquan came out of Xingyiquan and as such inherited all of the standing knowledge from that system. However, the founder Wang Xiang-Zhai believed that since standing was the core power development of the system, a faster and more efficient route could be taken by separating the standing component from the forms. As a result, things like the five element fist and the animal forms were removed in favor of more standing meditation practice.
Yiquan has the most developed and concise training material as well as the most prolific writings explaining such training out of all the other martial arts put together. In many ways Yiquan is the king of standing meditation. As such any investigation of standing meditation should consider deeply the principles of Yiquan before deciding whether or not they are useful for the art they currently practice.
I don't know anything about Bagua but if I find out something I will provide a link.