Is anyone out there using D for real world applications? If so, what are you using it for? I can't seem to find anything big on the web written in D.
Despite the lack of known big users, D seems like a very promissing language to me, and according to TIOBE, it's fairly popular.
Facebook announced that they are using it in production as of today.
The D's official website enumerates the organizations that are currently using D.
The D wiki also provides a list of organizations, but it's outdated.
Just watch carefully DConf talks.
Almost all people there work for some company, and they use D at work.
I'm using D in research about compile time code translation. The advanced templating combined with tuples and mixins makes code translation much easier and allows for code translation to be done during compile time without requiring a separate tool.
There are some examples of physicists using D to enhance their programs with meta-programming in D.
video - Conference talk, could not find source site of physicist use.
A lot of the games released by ABA Games are written in D 1.x, though I imagine the console ports had to be rewritten in C++.
I've written quite a few game prototypes in D, but I'm not sure if that qualifies as 'real world' since I wrote them for my own benefit and have never released any of them.
I used D for my research project on developing a global optimization algorithm. I applied it to the problem of training neural networks. It's up to you whether you want to call this "real world".
I use D for web development and it proved quite a lot more productive compared to C/C++. There are a lot of frameworks based on ruby/php/python, of course. But when you want to develop something unique that also have to be as fast as C and nearly as easy as to program with as you do in many script languages, then D is a good choice.