Lsyncd is designed to synchronize a slowly changing local directory tree to a remote mirror. Lsyncd is especially useful to sync data from a secure area to a not-so-secure area.
Mirror is an asynchronous synchronisation tool that takes use of the inotify notifications much like Lsyncd. The main differences are: it is developed specifically for master-master use, thus running on a daemon on both systems, uses its own transportation layer instead of rsync and is Java instead of Lsyncd’s C core with Lua scripting.
DRBD operates on block device level. This makes it useful for synchronizing systems that are under heavy load. Lsyncd on the other hand does not require you to change block devices and/or mount points, allows you to change uid/gid of the transferred files, separates the receiver through the one-way nature of rsync. DRBD is likely the better option if you are syncing databases.
GlusterFS and BindFS use a FUSE-Filesystem to interject kernel/userspace filesystem events.