OpenBSD_malloc_Linux.c:

    The OpenBSD malloc implementation, ported to Linux.  Used only when
    --enable-openbsd-malloc is passed to the configure script.

eventdns.[ch]

    A fork of Libevent's DNS implementation, used by Tor when Libevent
    2.0 or later is not available.  Once Libevent 2.0 is required, we
    should throw this away; it has diverged from evdns.[ch], and is
    no longer easily mergeable.

ht.h

    An implementation of a hash table in the style of Niels Provos's
    tree.h.  Shared with Libevent.

tinytest.[ch]
tinydest_demos.c
tinytest_macros.h

    A unit testing framework. https://github.com/nmathewson/tinytest