terminalizer is described as 'Record your terminal and generate animated gif images or share a web player'. There are six alternatives to terminalizer for a variety of platforms, including Linux, Mac, Windows, Online / Web-based and BSD. The best alternative is Asciinema, which is both free and Open Source. Other great apps like terminalizer are Scrimba (Free), showterm (Free, Open Source), ttygif (Free, Open Source) and ttyrec (Free, Open Source).
ttyrec is a program and/or its file format capable of recording the TTY output of a text-mode program together with timestamps and then replaying it. It is widely used for example in the NetHack community for storing game replays.