We might want to share here:

• Hacker News (Show HN, remember to read the rules before posting)
• Reddit
  • r/quantifiedself
  • r/coolgithubprojects
  • r/python
  • r/opensource
  • r/productivity
  • r/linux?
  • others?
• Product Hunt
• AlternativeTo
• Stack Exchange questions asking for time tracking software recs
  • https://productivity.stackexchange.com/questions/13913/linux-automatic-time-tracking-software-for-computer-work (disclose affiliation if creating an answer)
    • The productivity StackExchange has been closed
  • https://askubuntu.com/questions/4113/which-time-tracker-application-do-you-recommend
  • https://apple.stackexchange.com/questions/40631/is-there-a-good-automatic-time-tracking-tool-for-mac-os-x
  • https://apple.stackexchange.com/questions/123487/looking-for-a-decent-time-tracking-application-for-mac
• Maybe they care about this stuff here: https://softwarerecs.stackexchange.com/, no one has asked any question yet though so might be premature.
• @nikanar mentioned a few lists of RescueTime alternatives, one could try and get ActivityWatch into them.
• This page on Wikipedia
  • Make sure to disclose affiliation
• Quantified Self Facebook-groups
  • https://www.facebook.com/groups/quantifiedself/
  • https://www.facebook.com/groups/qssthlm/
• The Quantified Self forum
• A proper Wikipedia article (we're as of writing probably not notable)
  • I've created a draft here: https://en.wikipedia.org/wiki/User:Erik.Bjareholt/ActivityWatch
• Open source news sites
  • ghacks.net
    • 2019-09-26: They wrote about us! https://www.ghacks.net/2019/09/26/activitywatch-open-source-personal-activity-tracker-for-windows-linux-and-macos/
  • itsfoss.com
    • 2020-02-15: I've contacted them asking them to write about us
    • 2020-05-16: They've now written about us! https://itsfoss.com/activitywatch/
    • 2021-06-18: And again! https://news.itsfoss.com/activitywatch-0-11-release/
  • opensource.com
    • 2020-02-15: I've contacted them asking them to write about us
  • omgubuntu.co.uk -
    • 2020-02-15: I've contacted them asking them to write about us
  • fosspost.org
• Quora
  • "What is the best open-source time-tracking software?" (52 follows)
  • "Is there a free/open source cross-platform time tracking app for productivity?" (4 follows)
  • "Is there an open source app/website time tracking software for Windows?" (2 follows)

I'm pretty sure I have a list of more places where announcements would be appropriate. Unfortunately, I can't be bothered to find it right now since it's still a bit off.