The applications running on this decentralised OS will be able to communicate with each other, there will also be measures to “firewall” applications.
Applications use very common functions such as user/password, user interfaces, backend (database) management. This means that applications can share frameworks or libraries which make development faster, more secure and less technical. For example, applications will have their own secure database and file space on EOS. EOS will allow developers to create blockchain applications with which end users will easily interact with. Probably most users would not even know that they will interact with one when using EOS as this will be completely transparent to the users.