I asked this question on Twitter a while ago and wasn’t entirely satisfied with the responses. Let’s try to crowdsource some more here.
Possible places to announce a tool that is not specific to one wiki:
- Wikimedia Mailing List, aka wikimedia-l
- Wikimedia Space
- Tech News
- Tech Showcase
- Planet Wikimedia, if you have a blog you can connect with it
- Wikipedia Weekly group on Facebook
- The Signpost and equivalents in other languages
- village pumps of wikis where you estimate the tool will be most useful
- all village pumps, via MassMessage (requires special privileges); consider that untranslated messages may not be well received
See also distribution list, best practices for reaching out to projects in multiple languages, and news channels (comprehensive list, not all channels are suitable for tool announcements).