We have set up a web-based forum for ImageJ:
It is driven by Discourse, an awesome project designed by one of the founders of StackOverflow, and utilizing some of the same concepts.
We invite the community to check it out, and let us know what you think!
We resisted setting up a forum for a long time, since we already have too many mailing lists. However, Discourse overcomes many historical problems of forums—it is really a quantum leap forward for facilitating effective and civil discussion—so if it works sufficiently well, we could consolidate and replace the imagej-devel and fiji-devel mailing lists in one fell swoop.