(Also see: 10 Big Changes in OS X Yosemite)
In a keynote presentation, chief executive Tim Cook said this would make it easy to start tasks on one Apple device and to continue on another: "a seamless experience unparalleled in the industry."
Alongside the operating system updates, the California company the world's largest by market value unveiled HealthKit software to manage personal healthcare and HomeKit for home appliances.
Apple played to its audience at the conference of third-party developers, hoping to keep them enthused, informed and devoted when it comes to designing hip, fun or functional apps.
Cook devoted a chunk of the keynote to a software development kit he billed as the biggest release since the launch of the App Store.
Apple also debuted a programming language called Swift, to allow developers write programs that are faster, modern, safer and more interactive than they would be under its predecessor Objective C.
Doors opened by Apple for developers included letting applications once kept separate in "silos" work with one another.
Examples included a Bing language tool being able to swoop in to translate a Safari browser Web page, or being able to "pin" a Web photo directly from Safari to online bulletin board Pinterest.
Apple also opened up its recently introduced Touch ID fingerprint recognition capability to third-party apps, giving the potential for it to become a security feature in more programs.
HealthKit was said to provide a secure haven for data collected by devices such as fitness bands that track activity and sleep.
Health-related information can now be collectively managed on Apple devices which could then watch for signs of trouble and even fire off messages to doctors when warranted.
HomeKit would let iPhones or iPads be used as a centralized control for Internet-linked gadgets such as door locks, lights, thermostats and security systems.
"We thought we could bring some rationality to this space," Apple senior vice president of software engineering Craig Federighi said while demonstrating HomeKit.
Apple came up with a common network protocol, so not only can an iPhone be used to open smart locks, but virtual assistant Siri can dim lights and lower thermostat settings when told "Get ready for bed."
Apple also beefed up graphics and speed capabilities for games, which are consistently among the hottest applications on its mobile devices.
Apple has sold more than 800 million mobile devices powered by iOS; more than half of those being iPhones, according to Cook.
(Also see: 10 New iOS 8 Features Showcased at WWDC)
Capabilities being woven into operating software included one called "Continuity," which let tasks started on one Apple gadget be automatically handed off to another one nearby.
Calling Dr. Dre
Messages or calls can also be handed off between devices, a feature Federighi demonstrated by ringing rapper and entrepreneur Dr. Dre, co-founder of startup Beats that Apple recently bought in a deal valued at $3 billion.
"Now, your Mac is phone savvy," Federighi said while making a tongue-in-cheek "welcome" call to Dr. Dre to discuss when he should show up for employee orientation at Apple.
Versions of the new-generation operating systems were made available to developers at the conference but won't be publicly released until closer to the end of this year.
"Improvements in how Apple products work together in the family are huge from a customer perspective," Forrester analyst Frank Gillett told AFP after the keynote presentation.
"And the improvements under the covers are huge for developers."
Apple is tapping into talents of third-party developers to put its hardware at the center of hot trends in wearable computing and in integrating technology into appliances and locks, according to the analyst.
Because Apple makes all of its own devices, it can achieve a level of synergy between them that competing platforms can't match, Gillett said.