It is an Audio Splitter for microphone signal used for distribute this signal into several identical outputs with the same level. Thanks to its insulation by transformer, each output is insulated from others avoiding ground loops. This is a very important issue as the connected devices can have different ground references.
A Mic Splitter offers a direct output for Phantom feed from console and then can distribute an electrostatic microphone signal. Thus, one console can’t damage to another device as through a transformer is not transmitted the direct current signal DC as phantom power.
Also, microphone splitters usually are made of transformers which are protected with Faraday Shield. This protects from noise of electrostatic interferences, an issue to be reckoned with low level signals as the microphone signal.
The microphone splitters are typically passive audio splitters so that if you want a line signal, is required a microphone preamplifier before distributing the signal.