The upstream & original Minetest. Minetest is an open-world sandbox game inspired by Infiniminer. The site, minetest.net, is maintained by core Minetest developers & is dedicated to the topic of the game. The only area of the site that might stray is the Forums. But any sub-forums or threads should be marked as being off-topic.
Being that the game itself is open-source, anyone can go through the code & inspect it for potentially unwanted or harmful information. I would expect that if anything harmful were contained within a project as popular as this one, it would be regularly exposed & reported by the many watching eyes around the world. But I have never come across, nor heard of anything coming out of the upstream Minetest source that was designed intentionally for unethical or illegal purposes.
I have done some minor contributions as a mod creator, & I have not had any negative experience with the site. At most, I have received some (hopefully to be intended as constructive) criticisms on my mods in the forums.
As any site where one can engage with people around the world, the potential to get into confrontations with others should be considered. That is the nature of a worldwide communication system where most anyone who wants to, can be involved.
I only marked the site as "be cautious" in regards to children, because it is an open community. There are moderators to try & make sure that rules are followed. But it is not expected for every conversation to be filtered for children. There is also a popular licensing text that uses the acronym WTFPL which contains some very choice language. Many of the mods created by modders & posted to the forums contain the language of this text. It is a completely legitimate license & I only mention this so that parents can make an informed choice about allowing children to browse the site unmonitored.
Official site of the Minetest international community, a free game developed by volunteers and enriched by contributors.
I recommend this site to all those who discover this game to obtain texture packs, mods or subgames.
Had potential to be a good but has been taken over by children who think they are above the law and perform illegal activities and act as judge, juror, and executioner...wrongfully so.
Minetest is a full on rip-off of minecraft, yet they feel it is somehow original work. They perform their own justice on those they do not like by hacking users servers, attacking websites, posting personal user information and making threats.
To see proof, read the documentation: http://www.globeminner.com/minetest-attack/