It's the Adblock package for OpenWRT. The default selection is
adaway, adguard, disconnect, yoyo, which is 3 x 10k lists and one 30k list.
I see that it has support for compiling Steve Black lists but SB can vary 50 - 500k and I only have a router with 128 MB RAM. I'll have to experiment with the "standard" SB list, see if it fits and if it makes any difference.