Schism Tracker is a music editor that aims to match the look and feel of Impulse Tracker as closely as possible. This SourceForge project page is more or less abandoned -- current development is ongoing at schismtracker.org.
This program is highly recommendable. I've used Impulse Tracker since 1998 or so and Schism Tracker is more than a worthy successor. It does the trick for those who just want Impulse Tracker functionality, but also extends on some of the features Impulse Tracker didn't have (like allowing for more than 99 samples). Highly recommendable.