Even in the early days of mainframes, every vendor was all over the dial for operating systems and proprietary solutions. Programming languages were standardized to allow hardware vendors to compete with machines. The IBM System 360 was by far the most successful mainframe with the new 32-bit registers which make accounting etc very easy to handle.
Later on with the workstation market: Sun, IBM, Apple and others all developed their own operating system.
Oracle bought Sun mostly for the software assets. Oracle struggled with open source because management wanted more proprietary solutions. Open source ended up retaining MySQL and OpenOffice was mired before recovering. Java had so many security issues developers abandoned it is droves.
When Linux was released as free and open source, the FreeBSD backers jumped on board with the new GNU license. GNU is based on the idea of free open source software.
IBM and their AIX operating system has been generally abandoned as few shops still use the PowerPC processor anymore. Hyper-V is free but it limited to Windows licenses to manage it.
PowerPC is backwards so binary code is a lost cause migrating to x86. Available source can be recompiled. PowerPC uses big endian which Intel and AMD use small indian which is more natural looking when considering a memory map.
Today Apache Linux and MySQL are widely used for databases and websites. WordPress have become the most popular content management system. PHP developer jobs are in demand.
Windows Server is not as widely used as Linux. Many host their own server and use it directly or they may use remote desktop. Remote desktop can be moved to a data center which has become a large scale industry. Azure competes with AWS and Google has been generally forced to sit on the sidelines. IBM wisely bought RedHat which put them front and center in the cloud business.
Today Microsoft Windows is the most popular desktop operating system while Apple’s MacBook runs OS X. Linux is a very small sliver of the desktop market.