When comparing FreeDOS vs Haiku, the Slant community recommends Haiku for most people. In the question“What is the best laptop OS?” Haiku is ranked 31st while FreeDOS is ranked 43rd.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Open Source
GNU GPL
Pro Large and friendly community
You won't be let alone, any question submitted on FreeDOS forums will be detailedly answered in a few hours time.
Pro Compatible with MS-DOS apps
Pro Supports FAT32 partition
As opposite to every MS-DOS version equal or older than 6.22, or any DR-DOS version, you won't be restricted by a 2 Gb large FAT16 partition.
Pro Highly portable OS
It takes ten minutes to make a portable, USB FreeDOS drive, All you need is a USB device FAT or FAT32 formatted (128 Mb should be enough, but a 2 GB device would be better). First make a FreeDOS bootable USB drive with a program like Rufus (on Windows) or UnetBootin (on linux or Mac). Select it at boot and run fdisk to make a Primary DOS partition and install FreeDOS on it. Final step: reboot and run fdisk again to make the new partition active (optional: delete the installer partition). After that, the system is ready to boot with any computer.
Pro Extremely lightweight
Takes less than 10 seconds to boot.
Pro Easy to dual-boot, either with any Linux distro or Windows
If you install a Linux distro after Freedos, GRUB2 will automatically detect it. As for Windows, newer EasyBCD releases implemented FreeDOS and automatically recognize it.
Pro Very fast
Pro Beta has been released
After about 6 years since the alpha version, beta has been released on Fri, 2018-09-28. Check here for release notes.
Pro Only need 512mb ram
Pro Stability
Pro Runs perfectly on old Hardware
Cons
Con Unlikely going to be your PC main OS
If looking for a lightweight OS, and thinking of FreeDOS as a possible option, consider that it will only useful when having to deal with legacy software, or other dos-based programs still commonly used at workplaces. Nonetheless it's a fantastic solution for Retro-Gamers who still own a a supported sound card. However the lack of modern software makes it hard to accomplish common everyday tasks, such us opening a document written in UTF-8, not mentioning, obviously docx and pdf files. The best choice is to install it on a USB drive, in order to have a portable OS, with basic hardware and all your files (and if you want games) ready to be launched with every machine. Useful to edit partitions, as well as restore MBR, check errors, install a light bootmanager on any kind of FAT partiton of every IDE-mode compatible hard-disk.
Con Obvious lack of sound card drivers
If you own a sound card produced after than 2000, you won't find a driver to make it work.
Con No one uses it
It's a very niche OS that no one uses.
Con Unfinished
It's still in beta and quite unstable. Making it unsuitable for developing applications of any kind.
Con Language support is terrible

Con Small community
It is important when developing to be familiar with tools that other developers use. You can make any utility in any language you feel like, but if it's in an esoteric language that no one can read targeting a small platform that no one uses, then it was just something you did as a hobbyist, not as a developer.
This is not to say that Haiku isn't a great operating system to hack around on. Just don't delude yourself into thinking you're doing it to get familiar with tools that you need to know to be a better developer.
Con UI quite different to other OSes
