One way is to use a virtual midi device. In MAC it's built into the OS via Audio Midi Setup -> Midi Studio. In Windows it's via third party apps, "Virtual Midi" is one.
For example, sometimes I write algorithmic music apps in javascript (inside a browser like Chrome) and I want to listen to what I did in Logic. So I set up a virtual midi device on the Mac. and then set it as input in Logic, and I write to it via the browser. With midi you can either write to, or read from a virtual driver. So my Browser is sending information to the DAW that way. But you could do this between DAWs as well.