The Moon Tree Project is a link aggregator like reddit or hackernews. The big difference is that it is opensource, you can host your own Iron Tree server and it is decentralized.
It's like with emails. You can have an @gmail account or and @hotmail account and they will be able to send mails to each other even if it's not the same server / mail provider. With the Iron Tree project each server (hosted by anyone that want to host one) can talk to each other. You could host your own server, create an account there and answer to this post here which is in my server.
Imagine if from mastodon (or twitter) you could follow contents from some subreddit that you like (like /r/programming). This is what the Moon Tree Project can now do.
The Moon Tree Project has branches, which are the equivalent of subreddits. Anyone can post in these branches and each branches has it's own feed. The big idea is that branches are just an other kind of user. In the same way that you can search and follow @Gargron@mastodon.social you can find @email@example.com and follow it.
Following a branche will make you see everything posted to it. But there is a problem, for a branche with hundreds of posts per day your feed would easly be flooded and unreadable. In the future there will be support filtered branches that only have the top 10 or top 100 of the normal branche. For example, you could follow @bestOfDrawing@moontreeproject.org which could be configured as showing only the top 10 of the drawing branch.
If you want to keep up to date with the project, you can now subscribe to @firstname.lastname@example.org ;)
Everything about the state of the project, new versions etc…