Is there any software that runs exclusively on FreeBSD?

Is there any software that runs exclusively on FreeBSD (software that runs on FreeBSD but not on Linux, OpenBSD, macOS, or Windows)?

There can/will obviously be alternatives on other operating system to software that runs exclusively on FreeBSD but I still am curious.
From reading around, there is some sort of illegal leaked game server (METIN)
I am assuming that this happens to be FreeBSD only since that is what the original developers used. It is kind of like MaNGOS in that it serves the infrastructure for a large MMORPG game world.

Otherwise have a check out of some of the innovations by the PC-BSD guys and FreeNAS. Both of these have bespoke tools to take advantage of the FreeBSD OS. Other than that, one of the main points of FreeBSD is to be standard and portable, I suppose that includes it's applications running on other operating systems.
I also think you can consider exclusively launched video games for the PlayStation 3/4/Vita and the Nintendo switch to be exclusive software for FreeBSD as well since the system software for those video game consoles is based off of FreeBSD.
The NetApp NAS box software stack, including WAFL, only ships on their own FreeBSD variant. I have no idea whether there internal developers can also use it on other host OSes. On the other hand, that software is not free, nor does it ship as software; you have to buy the NetApp box to get the software.

There are probably several other FreeBSD based appliances, meaning their software only uses FreeBSD.

I think what you meant to ask is: Is there any freely available user application software that only runs on FreeBSD? Not to my knowledge.
Any open source project would likely not be "exclusive" to FreeBSD after some time had passed. It's too easy to port FreeBSD-Linux or Linux-FreeBSD. Bhyve and jails might be exceptions, but there won't be many of those ...
various jail and bhyve management tools

As most jail and bhyve management tools are only shell scripts or written in some interpreted language like python, they would actually run on other OSes - but without any jails or bhyve this would be rather pointless ;)

I don't know if jails can be considered an actual standalone software, as they are a concept within the FreeBSD kernel.

Although a lot of open source software got ported to linux, it's quite interesting - and sometimes amusing - what is available on all UNIXes BUT except Linux: E.g. dtrace is available on FreeBSD, illumos, OS X but not on linux - where you still have various different tools that kind of overlap but none of them is as flexible, thorough as dtrace and most importantly: NONE is production-safe and all have a massive impact on performance...
I once noticed Linux guy bitching in Phoronix that OpenSSH server needs "a lot of porting" for it to work in Linux.. For him it seemed BSDs are at fault.

Got little laugh out of it.
There are some programs that are exclusively built for FreeBSD, but they are usually small utilities for specifically managing or working with FreeBSD features. Stuff like Warden or swapexd deal specifically with FreeBSD features and wouldn't be particularly useful on other platforms.
In the same light, nginx was originally created on FreeBSD and was always maintained on FreeBSD until just recently when market pressures forced them to switch to Linux, something they've said they regret having to do.
Didn't know that about nginx. Lots of interesting things are developed on *BSD first, and are later used as references. Prime example of this is of course the TCP/IP stack :D

I can't really think of anything that would be exclusive to FreeBSD or BSD in general actually.