1. FreeBSD：
FreeBSD 是 FreeBSD 项目提供的免费开源操作系统。它是在两个类 Unix 操作系统 Berkeley Software Distribution (BSD) 和 Research Unix 的基础上设计的。它与 Linux 操作系统非常相似。它是早期著名的操作系统之一，但与其他操作系统相比，现在使用较少。 FreeBSD 的第一个版本于 1993 年推出。FreeBSD 的最新稳定版本是 12.1。
2. 操作系统/2：
OS/2 是微软公司和IBM 合作开发的一系列操作系统。它的目标系统是个人计算机和服务器。它是使用 C、C++ 和汇编语言编写的。 OS/2 的第一个版本于 1987 年推出。它于 2006 年停产，之后以 eComStation 的名称进行更新、维护和销售。 2015 年，它被命名为 ArcaOS。此操作系统中使用的内核是带有模块的 Monolithic。
OS/2 和 FreeBSD 的区别：
| OS/2 | FreeBSD |
|---|---|
| It was developed by co-ordination of Microsoft Inc. and IBM. | It was developed and is owned by The FreeBSD Project. |
| It was launched in 1987. | It was launched in 1993. |
| Its target system types are personal computers and servers. | Its target system type is server, workstation, NAS and embedded systems. |
| Computer architectures supported by OS/2 are 16-bit x86 (1.x only) and IA-32. | Computer architectures supported are IA-32, x86-64, ARM, MIPS and PowerPC. |
| Its kernel type is Monolithic with modules. | Kernel type is also Monolithic with modules. |
| Its package management is Feature Install. | Package management is Port collections and packages. |
| Its native APIs are Proprietary, DOS API and Win16. | The native APIs are BSD/POSIX. |
| It has the preferred license of Proprietary. | Preferred license is BSD. |
| File systems supported by OS/2 are HPFS, JFS, FAT, ISO 9660, UDF and NFS. | File systems supported are UFS2, ZFS, ext2, ext3, FAT, ISO 9660, UDF and NFS. |