A 4 serial solution is needed

I need a 4 serial communication board which can simultaneously communicate with four serial modules. So far the best solution within the arduino family is 2560. I am looking for some alternative ones. Any suggestions? I found stm32f107 supports that many serials. But is it supported by stm32duino? Is that family reliable?

Most of the SAMD21 Arduinos can run 4 or more Serial ports if you're able to give up other functions. (one port would be on the I2C pins, another on a couple of the Analog pins...)

I think you are dead right about that.