Sysinstall is the menu-driven installer that FreeBSD Release 8.x and older Releases used as a default. You see it during the inital install and you can run it at any time from the command line. The man page for sysinstall warns of the following bug:
BUGS This utility is a prototype which lasted several years
past its expiration date and is greatly in need of death.
With the start of the Release 9.x series the sysinstall menu-driven installer has been replaced with bsdinstall. It is not as full functional as sysinstall, but an companion bsdconfig script is scheduled for release in Release 10.0. In the mean time sysinstall has been cloned creating sade(4) which gives you the same configuration ability and is available in Release 9.x.