Communications
RZSZ is a toolset that provides command line tools for sending and receiving data using XMODEM (sx, rx), YMODEM (sb, rb) and ZMODEM (sz, rz). The source code is really old (pre-ANSI), but it was a relatively easy process to modify the code to compile for two different ARM devices. The ZMODEM protocol was developed by Omen Technology, Inc.; RZSZ can be downloaded from their site as well.
https://ohse.de/uwe/software/lrzsz.htmllrzsz is a free and open source version or RZSZ; in fact, the code base for lrzsz was forked from RZSZ.