In an unlikely scenario that beautiful Shiny apps do not meet your analytical requirements and developing a full-blown user interface. in RGtk2 may seem to be a little too much, there is a third, often overlooked solution, - package svDialogs by Philippe Grosjean. The package in a convenient way enables user to create various interface gadgets. For example the code:
require(svDialogs) # Let's keep some data in one place user_figure <- svDialogs::dlg_input()
would result in the following window being presented to the user:
In this case the code will return the following object:
str(user_figure) # Classes 'nativeGUI', 'textCLI', 'gui', 'environment' <environment: 0x11872b648> user_figure # The default SciViews GUI (.GUI) # using widgets from: nativeGUI, textCLI # * Last call: dlg_input(gui = .GUI) # * Last widgets used: nativeGUI # * Last status: ok # * Last result: #  "100"
The post was inspired by an amusing discussion on SO.