The below information was originally published on the Romraider forum. I have aggregated it here to hopefully make it more easily accessible.
To read it directly from the source, head to: https://www.romraider.com/index.php/Documentation/RomRaiderFAQ
To get started with Romraider, head on over to their site and download the application. You can also click on the button to the right to download it. You'll also need to download EcuFlash.
Romraider is what you use to edit your tune and create data logs. EcuFlash is used for flashing new maps to your ECU.
I highly recommend reading the Getting Started guide on their site as well, as it goes into more detail of what open source tuning is, risks, and how to avoid having problems.
Definitions:
Next, you will need to install the correct definitions for your ECU. Definitions are what allow the programs to interact with your ECU.
How Install Definitions:
Download one of the definition packs from the links to the right, you can choose from Standard units or Metric.
Unzip the ecu_defs.xml file into your main RomRaider directory replacing the existing file (if applicable) or in another directory of your choice where it is unlikely to be moved or deleted.
Open Romraider and select "ECU Definitions" -> "ECU Definition Manager" from the menu bar.
If any definitions files are listed, select each file and click "Remove".
Click "Add" and select the location of the new unzipped ecu_defs.xml file.
Click "Save".
Repeat the above process for the logger definitions as well.
When opening map files, Romraider will now be able to automatically determine the correct definition for your ECU.
If upon opening a file, the parameters are greyed out, you likely do not have the correct definitions or your ECU is incompatible with them.
Installing EcuFlash Definitions:
Download one of the definition packs from the links to the right, you can choose from Standard units or Metric.
Unzip the files and put them in a folder that will not be deleted.
Open EcuFlash and click on File -> Options -> Metadata Directory
Click the "..." and browse to the directory where you have placed the definitions you just downloaded. Selected the Subaru folder as your definitions directory.
You should now be able to open map files that end in .hex, .bin, and .srf and EcuFlash will automatically select the correct definitions.