library(dplyr)
library(tidyr)
library(ggplot2)
library(gridExtra)

df = data_frame(a = rnorm(100, mean=1), b=rnorm(100, mean=2),  c=rnorm(100, mean=0)) %>% 
  gather("var", "value", a,b,c)

ggplot(df, aes(x=value)) +
  geom_density(fill="black", col="white", lwd=1) +
  facet_grid(var~1, switch="y") +
  theme(strip.text.x=element_blank(), panel.background=element_blank(),
        panel.margin.y=unit(-3, "cm"), panel.grid=element_blank(),
        axis.ticks.y=element_blank(), axis.text.y=element_blank())