There are several places online in which announcements, discussion, and collaboration happen. Rather than tell you about them all at once, though, it's best to tell you which ones are relevant to you, given how you'd like to participate (or not) in the project.
Our primary methods of communication are mailing lists and IRC. If this isn't how you're used to interacting with free software projects, DON'T PANIC.
We provide instructions for how to get started, and several different interfaces for you to choose from depending on what workflow (web, mail, Atom, etc.) makes you most comfortable. Details of these will be explained further on, but first, you should figure out what communication channels are actually relevant for you.
If you want to post to the mailing list, and are not planning on using the web UI, you will need to disable HTML mail in your client. Instructions for how to do that are probably available for your mail client of choice.
If you're interested in keeping up to date with announcements from Spectrum's developers, you should subscribe to spectrum-announce. You can discuss Spectrum and related topics in real time on IRC, or more long-form on spectrum-discuss. Finally, development work happens in Spectrum's source repositories, and is discussed on spectrum-devel. There's another page that goes into more detail about contributing to Spectrum's development.
There is a single IRC channel, #spectrum on Freenode, for all kinds of Spectrum discussions. If you're new to IRC, you might find Freenode's web chat the easiest way to get started. The channel is logged, and the logs are published on the web.
If you're interested in participating in the project, or even just following along with it, the best thing to do is subscribe to one or more of the Spectrum mailing lists.
If mailing lists aren't your thing, that's okay! Try the web UI, which allows you to interact with the mailing lists much like a modern web forum.
Each list has archives that can also be accessed via the web, NNTP or Atom. You are strongly encouraged to mirror them.
This is a one-way list where announcements from Spectrum's developers will be posted.
You can subscribe on the web, or by sending mail to email@example.com.
This list contains high-level discussion about the project.
You can subscribe on the web, or by sending mail to firstname.lastname@example.org.
This list is for the nitty-gritty of development. It's where low-level technical discussions happen, and where patches are sent.
There's a separate guide for the Spectrum development process, including how patches are sent to this list and discussed.
You can subscribe on the web, or by sending mail to email@example.com.
You may distribute this content under the terms of either the CC-BY-SA license (version 4.0 or later), or the GNU Free Documentation License (version 1.2 or later), at your option.