For those who had developed applications with D,
I used tango libraries + dfl and a bit of my own. Tango documentation is excellent. DFL not bad. Yes I did use tango then but tried phobos at first. Ready for big apps? depends on what you mean. In production use I have only used it for frontends and updaters. So far I've only used vim to code and entice to design gui because I couldn't find the right ide for me.