D features - wanna start project

[toki]

Hi,
I love D, and after using Java for years I want to switch back to D.
I'm too lazy to google, and so wanna ask you.
1. Is D still under development ? Is it still supported ?
2. Which GUI lib would you suggest - which is the most robust implementation ?
3. Are there any OpenGL bindings ? Are they stable ?
4. I often use HashMap, HashSet, TreeMap, TreeSet. Do they have counterparts in D ?

Best Regards
Thorsten