IRTrans transceivers to transmit and receive IR codes, either LAN or USB modules
Apple IR Receiver, built into newer Macs, only suitable to receive IR from Apple Remotes
Serial Modules (not yet), mostly connected via USB-to-Serial adapters
You may rename modules if you have more than one, to distinguish transmitting and receiving modules. You may also temporarily disable modules. If a module is greyed out, it's a formerly connected module which could not be found at the moment.
If you have more then one module, please configure the default transmission and learning module in iRed's Preferences.