Easiest (secure, internal) dashboard / graphs?

So I don't want a lot of overhead but I would like to graph things over time. Obviously there's a ton of graphs and so on out there. What is the easiest / most flexible one? I am particularly concerned with being able to lock down access. I am thinking it could be easiest to just make a shared Google document with graphs. I'm particularly interested over time. it should be similar to if I just drew it by hand - nothing fancy.