#PieFed just added a multi-reddit feature, which we're calling "Feeds". It combines multiple Communities (actors of type "Group" in ActivityPub) into one.
Feeds can be followed from other PieFed instances, which will subscribe the follower to all the communities in the feed.
Try it out at https://piefed.social/feeds
It's similar to PieFed's concept of a Topic https://piefed.social/topics, except topics are maintained by the instance admins. Feeds are crowdsourced and federated topics.
GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.