Client software for your computer with one interface to access online discussion from Usenet, listservs and webboards.
Usenet is fading, but is still out there with a few groups interesting enough for anyone, for many it is just not worth to launch client software for.
Listservs, mailinglists
can still be very good, especially when you subscribe with a dedicated mailadres to it and you read it in an interface that displays threads properly. The discussions should not end up in your regular mailbox.
Webboards are the standard nowadays it seems. Because membership is required and the interface is easy it attracts the masses without the mess that Usenet 'freedom' gives.
The latter have the irritating technical disadvantage that a lot of redundant HTML-code needs to be processed by your browser, while it is just the same (ugly, clumsy) PHPBB or whatever interface all over, everywhere.
It just is not as 'snappy' as Usenet in a good client is. You also lack all the superior word processing features a local client can give you.
The client should check by itself all the discussions you want to participate in and retrieve everything you are subscribed to in the background. It also keeps a copy of your own postings locally and a few weeks of the incoming postings. You can easily mark a posting or an entire thread to save for later.