SAC
SAC is short for Seismic Analysis Code, and it is an old tool for looking at seismograms. I do not recommend SAC for modern studies of seismic data, but I use it frequently to get a quick look at some data (not always seismic data either). SAC was developed at the Lawrence Livermore National Laboratory in California, and is now painted and distributed by the IRIS community. You can find the official SAC pages here, and if you google for SAC and seismic, you will find many tutorials around the web. The book referenced on that page is available through our library. You can find it through this link.
My SAC examples can be found: