This photo of John Hakim's 5.5 gallon mini-reef aquarium pictures his Bi-Color Anthias, Cleaner Shrimp, White Stripe Maroon Clownfish, colony of Yellow Button Polyps, Red Mushroom, and Xenia soft corals.
Smaller tanks make great Do It Yourself (DIY) Projects. They are fun, easy, inexpensive and go together quickly. Just modify the DIY 55g Glass Aquarium Plans to meet your needs. There are a number of Canister and Power Filters and Mini/Nano Reef Tank Lights which will allow you to keep corals in your new tank.