Gemini is great for finding files that are the same. Diff at the terminal shows me files that are different. Is there a Gemini equivalent GUI that would quickly let me compare the differences between two similarly named files.

In short, the files on my production server are performing differently than the files on my dev server and I'm pulling my hair out. If I was on Windows, I'd be opening the dev file and the production file up in Notepad++ and using the compare feature to highlight the differences. Git and SVN aren't helping in this case.

Edit: Thank you all! These were exactly the answers I sought.