By default, Windows doesn't let you route one MIDI controller to two applications at the same time. So, To route MIDI data to both Syntorial and another application simultaneously, we recommend using loopMIDI:

1. Install loopMIDI

• First, download and install loopMIDI. 
• After installation, open loopMIDI. You will see a user interface that allows you to create virtual MIDI ports.

2. Create a Virtual MIDI Port

• In the loopMIDI interface, there’s a section to create new virtual MIDI ports.
• Click on “+” to add a new port. Name it something memorable, like “Virtual MIDI for Apps”.

3. Configure Your MIDI Device

• Connect your MIDI device to your computer and ensure that it’s set up to send MIDI data.

4. Set Up Syntorial

• Open Syntorial and go to Options → MIDI and Audio Settings.
• In the MIDI input section, select the virtual MIDI port you created (“Virtual MIDI for Apps”) as the MIDI input source.

5. Set Up the other application

• Open the other Application's MIDI settings and select the same virtual MIDI port you created (“Virtual MIDI for Apps”) as the MIDI input source.

6. Route MIDI from Your Device

• Depending on your MIDI device’s configuration software or capabilities, you’ll need to set it to send MIDI to the loopMIDI port (“Virtual MIDI for Apps”). This step varies greatly between different MIDI devices, so refer to your device’s user manual for specific instructions.

7. Test the Setup

• Play some notes on your MIDI device. You should see MIDI activity in both Syntorial and the other appllication, indicating that they are both receiving MIDI data from the same source.

This setup should allow you to simultaneously send MIDI data to both Syntorial and Reaper, making it easy to work with MIDI in both applications at the same time.