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This is a utility I wrote years ago (when cu's clunkiness drove me crazy enough). It lets you type to an attached RS-232 device. These days, it'll be something on /dev/ttyUSB0 with a USB-to-serial songle.
Although not as useful as it used to be, it has hooks to X- Y- and Z-modem programs to do transfers over serial. It can also log your data as it comes and goes.