On the seventh day of Pesach I went to Chabad for morning services. I've only been there a couple times before (always on a chag), so I'm not very familiar with their customs. At the end of each of the services I've been to, after Ein Keloheinu and Aleinu and Kaddish Yatom, there was a reading from Tehilim. When the rabbi announced it this time he said something like "today is Nisan 21, so the reading is (page number)". If I recall correctly, for that day it was Psalm 104.
This last part was not in their siddur; we used separate books of Tehilim. I don't know if that's just how it's done or if this means that what they did isn't normative -- I've only been to the one Chabad community.
What was that about? This wasn't the regular psalm for the day (Monday in that case); it sounded like this was something tied to date, not day of week, and anyway if it was day of week it wasn't the usual text.
(I hope to ask the rabbi about this at some point, though I don't see him that often. But I thought I might get a faster answer here.)