Soooo… Months ago I started working on ESP8266 based projects. One of them is a simple PCB with a connector for mains voltage in, 100mA fuse on to provide a bit of protection, switching power supply to convert the mains power into 5V DC, a LDO linear 3v3 regulator to bring the 5V down do a voltage the ESP8266 likes, two n-channel mosfet to drive the relay, relay terminals for connecting something, and then of course the ESP8266 itself.
The board isn’t made for something specific, so if I don’t need the relay, I just leave the components for that out, and use the 1×4 headers at the bottom of the PCB instead. And if I don’t need mains power, 5V can just be connected to the + and – terminals that normally are under the power supply.
Files for the board will be on Github soon(tm).