PCBoard was a popular bulletin board system (BBS) program in the 1980s and 1990s. Unlike some others (e.g., Fido BBS and Opus-CBCS), it was not free to use, but was commercial software that needed to be purchased and licensed for its intended use, with licensing fees increasing with the number of phone lines of the BBS. It was considered a high-end BBS program suited for professionally run BBSs. The final released version was version 15.3 in 1996, with a beta version of 15.4 coming out in 1997; like most BBS-related things, the widespread use of the Internet in the late 1990s put an end to it.
PCBoard text graphics
A format of text-based graphics similar to ANSI Art was used with PCBoard, perhaps sometimes stored with a .pcb extension (though ones actually used in PCBoard BBSs, as mentioned in the program's documentation, had different extensions or no extension at all). Finding documentation on this and other aspects of the PCBoard software is difficult, since searches on "PC Board" or "PCB" tend to give lots of results pertaining to printed circuit boards.
The format was generally ASCII, with embedded macros consisting of words in between two at signs (@), sometimes with parameters separated from the macro name with a colon (:). Colors were set using an at sign followed by X and two hex digits for the foreground and background colors (no closing @ was used after this). The CUSTBBS.DOC file in the PCBoard documentation lists these macros. (You can find that in this file; first, unZIP the downloaded file, then the actual docs are within a self-extracting EXE; if your operating system can't natively run such old DOS executables, you can rename its extension to ZIP and unzip it to get the .DOC files, which are actually plain text rather than MS-Word.)