Slackel is maintained by one guy living in Greece, who's describing it as a distribution and Live Cd based on Slackware and Salix, which itself is based on Slackware. It is based on the latest snapshot of the current development tree and combines it with the latest KDE which I understand is the one Eric is making available. So that's doing all the fiddly work of upgrading manually for ya. It also offers additional repositories to Slackware and Salix users as they are all compatible. Nice stuff, and it also comes with a few extra goodies like the Bangarang media player and Clementine replacing Amarok, but not too much extra fluff to annoy the Slackware purists in my opinion. Both live and install images are available from the main page, in 32- and 64-bit. The Live images are built with SaLT (Salix Live Technology) and are also installable. The Live images offer a GUI installer. The Salix multimedia codec installer can also be used to quickly get these, including Flash, onto your system.
Apparently Slackel has been around since the Slackware 13.1 days, providing a newer KDE, but this announcement on DistroWatch is the first time I heard about it. According to this post on Eric's Alien Pastures blog KDE may also soon be updated in Slackware proper, taking it from 4.5.5 to 4.8.2. Just make sure you run it without Kontact/Kmail and whatever that indexing service is called Kmail and that PIM suite seem to rely on.