Maintaining metabolic homeostasis requires regulation of blood sugar levels. After you eat a meal, your blood sugar levels increase. This triggers cells in your pancreas to release insulin.

Insulin binds to insulin receptor on tissue cells and tells them to absorb glucose. That results in a decrease in blood glucose levels.

When you have not eaten for an extended period of time, your blood glucose level drops and that triggers the pancreas to release a hormone called glucagon. Glucagon signals to the liver to produce glucose from stored glycogen and release it into the blood. The result is an increase in blood sugar.

The balanced release of insulin and glucagon is an import system to maintain homeostasis. When this system is disrupted, people develop diabetes. Interestingly, some animals have dysregulated glucose homeostasis as a part of their normal physiology. I just published a paper describing blood glucose regulation in the Mexican cavefish. Populations of this fish that evolved in caves are unable to regulate blood glucose, yet they are healthy. You can use this link to check it out! cavefish blood regulation

blind cave fish diabetes

I could just say "all of them" and it would not be far from the truth. The skin keeps fluids in and the air out. The respiratory system helps get the elements out of the air that are needed, as well as expels some waste products. The digestive system brings other materials not part of the air in, and excretes unwanted detritus. The excretory system removes more waste products. All of it is coordinated by the nervous system. The skeletal and muscular systems enable movement in order to get necessary materials. Really the only system that I can't think of in maintaining homeostasis in some way is the reproductive system.