On piefed you can join :

• Peertube channel : https://tarte.nuage-libre.fr/topic/peertube/mondelibre and crosspost them.
• in late 2025 : follow mastodon account.
• follow Pixelfed : not supported.
• later in 2026, mobilizon : we can create event post. The base is ready for futur federation with mobilizon : https://codeberg.org/rimu/pyfedi/issues/291

On mbin, you can join :

• peertube channel
• mastodon account
• pixelfed (probably supported but i don't know well mbin)

Lemmy

• peertube : i got bad result with peertube but maybe over time they solved it, i haven't retested it. It was possible but you had to manually retrieve the video
• mastodon : not supported.

People from mastodon, pixelfed...can post on lemmy, mbin, piefed. They need to mention the forumverse community. Eg :
@forumlibre@jlai.lu

I often recommand this formatting on mastodon :

The first paragraph will be the title

And i chose the community where i would like to post, eg : @forumlibre@jlai.lu

The second paragraph will be the body text

#someHashtag

Another note : markdown may not be supported accross fediverse software. For example : https://piefed.social/post/1004603