I have encountered the Disqus forum module on one site and would like to install it on my own website. 
However, I noticed on https://backdropcms.org/project/disqus that the Disqus module has not been updated since 21 Aug 2015.
Is there a reason for this? Was that module so well designed back in August 2015 that it has not needed any updates for almost 7 years now?
Are Disqus-style forums become less popular now?
Is there some other reason that such forums should not be used?
... or are there better alternatives to Disqus?
Thank you for your attention.
 candobetter _dot_ net
The quick and unfortunate answer to your question is that the module has no maintainer. The person who ported the module is no longer active in the community and the module is listed as "seeking a maintainer."
If a module is listed as "seeking" a maintainer, anyone can take it over and help update it or add new features if they are an approved member of the Backdrop Contrib Group.
But, unless someone is willing to take care of this module it is unlikely to receive any updates and you should take that into consideration before using this module.
I notice that this module only has 7 active installs, which does indicate a lack of interest in this module. However, this does not mean that disque forums are necessary unpopular, it might also simply be that forums in general are used less frequently on Backdrop sites than they used to be in the Drupal 7 world.
For more information, see here:
Other projects of possible interest:
A project in development:
Thank you for clearing this up for me.
Maybe I should find out how well the Disqus module is working on those 7 active installs. If it is being used a lot on some of them and problems have not been encountered, then perhaps I could assume it is safe for me to use in spite of it not having been updated in 7 years.
@cacofonix - Personally, the mere fact that a module has not been updated in 7 years is not necessarily a bad thing in my mind. I would do a little testing to see how it works before making a decision.
Also, be sure to check the issue queue for the module to see if others have reported problems.
If it's a module you really want to use and you are not able to help maintain it yourself, you might want to connect with the Backdrop Community during our upcoming Backdrop LIVE event OR in our https://backdropcms.org/supportZulip chat channel to see if anyone else has experience with it or might be willing to take on maintainership.
stpaultim, thank you for the feedback. I have noted Backdrop LIVE event on my wall calendar (not yet having decided what sort of digital calendar to use) and will attend if I am able to.
You have persuaded me to give Disqus a try, thank you.
As for maintaining Disqus, I am considering it, but it's somewhat a matter of that priority versus a number of others for me. I have some years ago worked as a Java programmer and many, many years before that in PL/1, and, I suspect, like many people here, have dabbled in a few other languages as well - C, C++, C#, Perl and Bash from my recollection. Back in the late 1990's I administered one of the first rural dial-up Internet Service providers in Warwick, Queensland - FlexiNet.