• show default Packages:
    > getOption("defaultPackages")
    [1] "datasets"  "utils"     "grDevices" "graphics"  "stats"    
    [6] "methods"  
    
  • currently loaded packages:
    > (.packages())
    [1] "stats"     "graphics"  "grDevices" "utils"     "datasets" 
    [6] "methods"   "base"     
    
  • show all available packages:
    > (.packages(all.available = T))
     [1] "base"         "boot"         "class"        "cluster"     
     [5] "codetools"    "compiler"     "datasets"     "foreign"     
     [9] "graphics"     "grDevices"    "grid"         "KernSmooth"  
    [13] "lattice"      "MASS"         "Matrix"       "methods"     
    [17] "mgcv"         "nlme"         "nnet"         "parallel"    
    [21] "rpart"        "spatial"      "splines"      "stats"       
    [25] "stats4"       "survival"     "tcltk"        "tools"       
    [29] "translations" "utils"       
    

    or command “library()” gives similar output – but if you are using RStudio output of “library” command will be displayed in other window