Naschmarkt

I see no one has answered this. As far as I know, the Naschmarkt is open year round. It consists of lots or different traders, all selling their particular range of food. For example, I remember lots of different Asian food stalls (with seating, like mini-restaurants.) I

I was there in December a few years ago. Yes, open.

The Naschmarkt has become very touristy, i.e. more and more restaurants replaced the old market stands.

The new market hotspot in Vienna is the Brunnenmarkt (in Brunnengasse and adjacent Yppenplatz); easily reachable by tram 46 (stop Brunnengasse).

From the videos I've seen it's basically now a big open air shopping mall and built for tourists, so yes

Yes, it is open all year except Sundays and holidays. Are there better markets that are authentic, yes.

If you plan it right, and have an interest, you might include a visit to the wonderful Third Man Museum, very close to the Naschmarkt. Not just about the movie but a fascinating and lovingly curated glimpse into post WWII in Vienna, and it takes perhaps an hour to tour.

I was on a recent Best of Munich, Salzburg and Vienna tour. On Saturday we went to the Third Man Museum, and stopped for a break at the Naschmarkt - just enough time for a delicious and refreshing Eiskaffee! Worth a visit.

If open food markets and farmers' markets are what you're seeking:

The Brunnenmarkt in Vienna's 16th district and Kutschkermarkt in the 18th district are two of the city's oldest street markets. Not only were there lots of people from all over the world, the variety of colourful fruits and vegetables, meat, bread, choice things to eat, etc. was plentiful and phenomenal. (I visited these two markets for a look, sip, and a nosh in late-spring.)

Vienna Info descriptions in English : Brunnenmarkt - Kutschkermarkt