WikiActivity is working now, at least it worked for me.
The Visual Edtior--Source mode usually works pretty well and has most of the features of the old editor. The category module is only available in Visual mode, but you can switch back and forth between Visual and Source without leaving your edit session. It has Find/Replace and an image upload (also mass image upload), and so on.
If you were not already aware, please read this blog post about changes that are coming. Specifically, the Forums, Message Walls, and Article Comments are being replaced by newer tools. For a detailed FAQ about the Forums retirement, see this post.