@jonny Depends who you are targeting. There are many options for #R IDEs:

For power users, the #ViM plugin Nvim-R would do https://www.vim.org/scripts/script.php?script_id=2628 or the #emacs ESS https://ess.r-project.org/

For a GUI-based R IDE (shows plots), there's #rattle https://rattle.togaware.com/ with a GPL-3.0 license and packages for #Ubuntu and others.

I also hear good things about #r4intelliJ for IntelliJ IDEA which can show graphics http://holgerbrandl.github.io/r4intellij/

And GUI-based #RAnalyticFlow http://r.analyticflow.com/en/ (LGPL)