in the community break-out session during this year's RIOT Summit, we discussed options to give RIOT projects more visibility. We now have a channel on hackster.io: https://www.hackster.io/riot-os/.
There are already some RIOT projects published, https://www.hackster.io/search?i=projects&q=riot-os. Please, link to RIOT if you publish on hackster.io.
And if you have a GitHub repo that relates to RIOT, please, add a "riot-os" tag as this makes it easier to find RIOT code, see https://github.com/topics/riot-os. Thanks to Jelle for bringing this up!