[1] - https://freenode.net
There is also CS StackeExchange for those open-ended questions that are in the area of theory.
Personally, I recommend good old Usenet. comp.programming newsgroup and others.
Instead there's just a fragmented bunch of relatively small forums, group chats, mailing lists, etc.
The traffic is pretty low on Usenet these days. You can blame your aforementioned fragmentation for that. People would rather write to walled gardens. The idea of using special client to connect a server is somewhat alien to the generation that equates the Internet with the Web. There is also a learning curve to Usenet. For instance, newbies will be dismayed by a long delay while the client downloads the the entire list of newsgroups when connecting for the first time. This is something you can turn off. E.g. in the SLRN newsreader's .slrnrc file:
set read_active 0 % don't download active file
set check_new_groups 0 % don't bother me with new groups
comp.compilers
comp.lang.awk
comp.lang.lisp
comp.programming
comp.programming.threads
comp.std.c
comp.terminals
comp.theory
comp.unix.admin
comp.unix.programmer
comp.unix.shell
sci.electronics.basics
sci.electronics.design
sci.electronics.repair > The idea of using special client to connect a server is somewhat alien to the generation that equates the Internet with the Web.
Walled gardens also have the attraction of having a more user-friendly experience that can work across a variety of devices. The last time I was even moderately active on USENET, I was slurping newsgroups via a scheduled job running Souper and reading/writing posts on Yarn, a console mode program for OS/2. I'm fairly sure SLRN is console mode as well... not really a selling point on today's technology, where many people would be using their phone/tablet.
http://www.linuxquestions.org/questions/programming-9/
you can ask whatever questions you want, and even ask a half formed question and eventually work out an answer through a back and forth
the community is great, and will happily help with the whole spectrum of questions from broad discussions to very specific individual software issues
i found offering an opinion in other peoples' questions to be as equally rewarding as asking my own
i linked to the programming forum above, but they have a bunch of great forums.. check out some of the other ones where you might have, or want to have, an overlap in interest:
They have been around for a while now http://www.javaranch.com/JRhistory.jsp