I'm probably missing something totally obvious, perhaps not, but how does one learn for example what scuttle or sme.mailsorting are and if they solve a problem I may need to resolve?
Well as the old saying goes.... You'll know what to do with it if you need it.
You start by reading the forum (or using the search function) and looking for contribs or announce threads. Some of this software (if not all) is available trough repos (most of it in testing) or on
www.contribs.org/contribs (same content only shorter link). So if you need something dig trough the forum. The contribs wiki is not well documented but they are only a few people maintaining it.