Although the need for software to be open is not a technical requirement, it is increasingly becoming a business requirement. Open means three things:
Open source: While there are numerous benefits of open source software, the key advantages are the users' ability to influence the direction of the project, the velocity of innovation, reduced license fees, and the ability to switch vendors.
Open APIs: To avoid vendor lock-in, the APIs must be open. Often, proprietary APIs are enticing upfront but lock users in.
Agnostic to underlying hardware choices: To reduce hardware costs and maintain users' preferences, the software needs to be hardware agnostic.