IPBT is a ttyrec player written by Simon Tatham, author of PuTTY. It is easiest to run on Unix, but can be made to work on other operating systems. The name is an acronym, expanding into It's Play-Back Time. There are several good reasons to use IPBT: it allows you to rewind files, it allows you to play at linear or logarithmic speeds, it allows you to jump to specific frames. The disadvantage is that IPBT must load the entire ttyrec file before it begins play; this is less of a problem for NetHack than for large, repetitive games like Angband.