I'm currently using one of MiniDSP's Dirac Live boxes, which corrects both frequency and time domains.
My system is pretty basic - homemade speakers using Alpair 10.2 full-range drivers, FLAC rips on a PC played through Foobar2000, and a tpa3620-based chip amp.
The Dirac Live correction makes a profound difference. This is in a rented pre-war NYC apartment, which isn't optimal acoustically. I can't play loudly, so also dialed in some "smiley face" EQ.
It's night and day better with room correction.
Before that, I used MathRoomEQ, a plugin for Foobar2000. That made things better, but Dirac Live puts more there, there.