Modern aquarium controllers, like the Neptune Systems Apex, are modular controllers full of features and WiFi connectivity for remote management. The base Neptune Apex controller is a small computer with an aquarium light timer, a temperature controller, a pH controller, and aquarium monitor. Additional modules include an automatic fish feeder, an aquarium doser, and even the Neptune Apex Trident water analyzer that tests your fish tank for calcium, alkalinity, and magnesium. The GHL controller is a similarly full featured aquarium controller that can be combined with with the GHL doser.
Marine Depot also carries single parameter aquarium controllers, like the American Marine Pinpoint pH controller, which is great for controlling a calcium reactor.