The Communications Toolbox, generally shortened to Comm Toolbox or CTB, was a suite of application programming interfaces, libraries and device drivers for the classic Mac OS that implemented a wide variety of serial and network communication protocols. Using the CTB, one could write an application that would seamlessly work over AppleTalk, a modem or any variety of other connections. Developers could also write plug-in communications modules known as "Tools", allowing any CTB-aware application to use that connection method.