eserial is the (RS232) serial interface code from eppp (circa 1996..1998), which will be brought up to today's (circa 2009) standards.
For compile+install, see the INSTALL file.
For how to use eserial... see the source code, which is almost certainly going to change.
Not usable. Needs adaptation to modern systems, bugfixes, code audit, API cleanup/redesign, and probably more.