Notepad++
Notepad++ can have very basic support for syntax highlighting igor files.
To install Igor support, perform the following steps:
Download syntax definition XML from https://raw.githubusercontent.com/igorlang/igor/refs/heads/main/extras/userDefineLang.xml
In Notepad++ go to Language/Define your language… menu, press Import… button and browse to the userDefineLang.xml you’ve just downloaded.