IntelliJ: https://github.com/JetBrains/intellij-community
PyCharm: https://github.com/JetBrains/intellij-community/tree/master/...
Android Studio: https://android.googlesource.com/platform/tools/adt/idea/+/r...
Yes, they might offer extended proprietary editions/plugins in addition, but the IDEs themselves are open source.
this is why i've built all of my setup using a dotfiles-like approach with the explicit intention of always being agent/model-agnostic: https://github.com/ma08/botfiles
the key insight is that if you own the context layer and keep your skills, hooks etc. portable enough, it's actually very easy to swtich agents at will (even mid-task)