Demo Radar chart app from http://glimmer.rstudio.com/mbannert/radar_chart/

server.R

data_sets <- c("mtcars")

shinyServer(function(input, output) {
  
  # Drop-down selection box for which data set
  output$choose_dataset <- renderUI({
    selectInput("dataset", "Data set", as.list(data_sets))
  })
  
  # select a car
  output$choose_car <- renderUI({
    selectInput("car","car",as.list(rownames(get(input$dataset))))
  })

  
  # Check boxes
  output$choose_columns <- renderUI({
    # If missing input, return to avoid error later in function
    if(is.null(input$dataset))
      return()
    
    # Get the data set with the appropriate name
    dat <- get(input$dataset)
    colnames <- names(dat)
    
    # Create the checkboxes and select them all by default
    checkboxGroupInput("columns", "Choose columns", 
                       choices  = colnames,
                       selected = colnames)
  })
  
  
  output$radar <- renderPlot({
    source("radar.R")
    webplot(get(input$dataset),
            which(rownames(mtcars) == input$car), y.cols = input$columns,add=F)
  })
  
  # Output the data
  output$data_table <- renderTable({
    # If missing input, return to avoid error later in function
    if(is.null(input$dataset))
      return()
    
    # Get the data set
    dat <- get(input$dataset)
    
    # Make sure columns are correct for data set (when data set changes, the
    # columns will initially be for the previous data set)
    if (is.null(input$columns) || !(input$columns %in% names(dat)))
      return()
    
    # Keep the selected columns
    dat <- dat[, input$columns, drop = FALSE]
    
    # Return first 20 rows
    head(dat, 20)
  })
})

ui.R

shinyUI(pageWithSidebar(
  
  headerPanel("Car Comparison Radar"),
  
  sidebarPanel(
    uiOutput("choose_dataset"),
    uiOutput("choose_car"),
    
    uiOutput("choose_columns"),
    br(),
    a(href = "http://statisticstoproveanything.blogspot.de/2013/11/spider-web-plots-in-r.html",
      "Radar by Alan Vaughn from statisticstoproveanything"),
     br(),
    a(href = "https://gist.github.com/mbannert/9124890/",
      "Find the shiny code gist here.")
    
  ),
  
  
  mainPanel(
    
    plotOutput(outputId = "radar", height = "600px"),
    tableOutput("data_table")    
  )
))

Okay, I got it. I just had to run together the webplot function available at: http://statisticstoproveanything.blogspot.de/2013/11/spider-web-plots-in-r.html