Nils Wogram has put together a trombone quartet and released Developing Good Habits on his Nwog Records label. Here's an excerpt from my review:
"...Developing Good Habits is an engaging, multi-textured record. It’s fascinating to hear how lines get introduced, extended, blended and developed between the four players. Some of the record brings to mind a swaggering Ellington brass section, and some of it a classical chamber quartet. The group doesn’t get into a lot of extended techniques, but they’re not missed, as the quartet generates a nice full, rounded sound with intricate arrangements that support solo passages."
You can read the full review of Developing Good Habits on improvised blog.