In our new home we have a set of french doors in our front room and a single door with glass that goes to our porch. I love the look of french doors with curtains so I plan on making these as soon as we move in. I found a couple good tutorials on how to make them.
All you need is some fabric and one of these curtain rods, it's temporarily out of stock but you could probably find one at a local sewing store, Lowe's or Home Depot.
It's called a sash rod
here is the fabric I'm looking at from fabric.com
I also like these ones, they are a bit lighter and may let in more light since they aren't the heavier home decor weight
I think I'd hang this one vertical rather than horizontal