https://en.wikipedia.org/wiki/Planet_(software) is a converter from RSS XML into HTML. It takes an RSS feed as input and generates HTML code plus the CSS style sheet as output. The generated HTML site is hosted in the internet for example planet Gnome, http://planet.gnome.org/
What most people doesn't know is, that the planet software can be seen as an autoposter. It takes the existing RSS feed and converts ALL entries into postings. The difference to a real autoposter is, that the HTML code is not directed to a different website, but is put direct to the webserver. This forbids the user to write a comment.
In theory, the planet software can be modified a bit. Instead of generating HTML output, it is possible to produce markdown syntax. The script for doing so is 10 lines long and was posted in a previous posting here in the same blog.
What makes planet unique is, that from the perspective of an autoposter it is a very aggressive bot. A dedicated autoposter bot has the ability to adjust in detail the schedule. Most autoposter are creating not more than 1 posts a day. While the planet gnome project is flooded with the complete RSS feed. If in the underlying blogs new content was created all the headlines are submitted to the planet gnome website. This is not done in delay but as soon as possible. So we can name the planet software the most radical autoposter ever. It can't be slow down, not it can't be filtered.
If the Planet software would be used in Google+ groups the chance is high that the user would be banned soon. The reason is, that the planet gnome RSS feed contains to much information. On a single day up to 5 postings are generated. The reason is that the gnome community is a bit chatty and produces a lot of news.
Somebody may ask what the meaning of the planet gnome project is at all. If the content is available in the referenced blog why is a dedicated frontpage created to combine all the content? Wouldn't it be more pleasant if the user will subscribe each blog individual and combines the RSS feeds in his local computer? The main reason why the planet software and the planet gnome project was realized is because of the needs of the bloggers who are producing the content. They want to be part of a larger community. They want to see, that it makes a different if they are positing a new article about a gnome related project. They want, that the other bloggers from their community will be aware of it and they want to informat the general public what is going on in their community.
The planet gnome project was created to unite the gnome community and to form a hub for communicating with the outside world. The literature call such an attempt a social network. Social network is equal to content aggregation. It combines decentralized content into a single website. From a technical perspective a social network is a playlist. It contains of URLs which are directing to the content. Social networks are very similar to a newspaper. The main task of a newspaper is not to write articles. But to curate existing content.