Some folks who use nand2tetris also like Logisim (I've used Logisim to teach digital logic for many years). I was saddened when I learned that the Logisim programmer, Carl Burch, was no longer able to work with it, so Logisim has not been updated in several years. However, a new group has forked Logisim and have made a number of significant improvements. If you are a fan of Logisim, you may want to take a look at the new fork: Logisim Evolution. You can find it on SourceForge: http://sourceforge.net/projects/logisimevolution/.
Cochise College, Sierra Vista, Arizona