sane-announce is a low-traffic list for release and similar announces. It's intended for users who want to know when a new release or beta snapshot of sane-backends or sane-frontends becomes available. The list is moderated. You don't need to subscribe to sane-announce if you read the sane-devel mailing list as all postings going to sane-announce will be posted to sane-devel, too. You can subscribe, unsubscribe or modify your settings by using the web interface.
There are message archives for sane-announce as well.
sane-devel is the discussion list for anything SANE (Scanner Access Now Easy) related. Despite its name, it's also intended for users. You need to be subscribed to be able to send mail to this list. If you are not subscribed, your mail may be approved by the moderator but that can take some time. When answering to a posting, keep in mind that the response is directed to the author by default. If you want to respond to the list, please use the "reply-to-list" (or similar) function of your mail client. You can subscribe, unsubscribe or modify your settings by using the web interface.
There are message archives for sane-devel as well. These go all the way back to April 2001 but for messages sent before August 2001 you're better off consulting the old archive.
sane-standard was used to discuss the SANE standard. Topics were the development of a next version of the standard and missing features and bugs in existing SANE standards.
The list saw extremely little traffic for years and was discontinued during a mailing list migration in April 2018. The list's archives are, of course, still available for your perusal.
sane-commit was used to distribute email containing a summary of changes for any push to the SANE git repositories. These mails were not archived. After all, a git log on an up-to-date checkout will tell you pretty much the same.
Times have changed and now the SANE git repositories are hosted on GitLab.com. We no longer send commit summaries to a sane-commit list. If you are still interested in following the changes of one or more of the SANE Project's repositories, we suggest you subscribe to the RSS feed for "Push events" of the repositories you're interested in.
You can also subscribe to the mailing lists by sending a mail containing the word "subscribe" in the subject to firstname.lastname@example.org (exchange devel by the respective list name). To unsubscribe, send a mail containing "unsubscribe password" to that address. You get the password by email once you have subscribed. If you lost your password, use the web interface to get it send to you again.
The SANE IRC channel #sane (irc.libera.chat) is intended for discussions about SANE and for getting help. Please be patient, answers can take some time. Please read the documentation before asking. Tell us which scanner, which operating system and which version of SANE (scanimage --version) you use.