Just started looking around, but Home Depot doesn't seem to carry anything like this, so I'll try what the last person posted, from the UK company. Sounds promising.
I really want the top-down solution so in the summer (even winter), I can just slide down the window and shade/shutter/blind/whatever, breath the fresh air, let the steam out the top, and still have privacy from the shoulders down.
We looked into the in-window shade, but (at least) Pella and Anderson only does it with their high-end windows, which are wood-framed only - not a good idea for a shower window. We really had to keep a vinyl framed window and so were left with no options.