IDE alternatives for R programming (RStudio, IntelliJ IDEA, Eclipse, Visual Studio)
RIDE -   R-Brain IDE (RIDE) for R &amp; Python, Other Data Science R IDEs, Other Data Science Python IDEs. Flexible layout. Multiple language support.
Jupyter notebook -   The Jupyter Notebook App is a server-client application that allows editing and running notebook documents via a web browser. The Jupyter Notebook App can be executed on a local desktop
Jupyter lab - An extensible environment for interactive and reproducible computing, based on the Jupyter Notebook and Architecture.
Radiant – Open-source platform-independent browser-based interface for business analytics in R, based on the Shiny package and can be run locally or on a server.
R Tools for Visual Studio (RTVS) -
A free, open-source extension for Visual Studio 2017, RTVS is presently supported only in Visual Studio on Windows and not Visual Studio for Mac.
Architect -  Architect is an integrated development environment (IDE) that focuses specifically on the needs of the data scientist. All data science tasks from analyzing data to writing reports can be performed in a single environment with a common logic.
displayr - Simple and powerful. Automation by menu or code. Elegant visualizations. Instant publishing.
Collaboration. Reproducibility. Auto-updating. Secure cloud platform.
Rbox - This package is a collection of several packages to run R via Atom editor.
Use below for more IDEs:
RKWard - an easy to use and easily extensible IDE/GUI for R
Tinn-R - Tinn-R Editor - GUI for R Language and Environment
R AnalyticFlow - data analysis software that utilizes the R environment for statistical computing.
Rgedit - a text-editor plugin.
Nvim-R - Vim plugin for editing R code.
Rattle - A Graphical User Interface for Data Mining using R.
How to Turn Vim Into an IDE for R