NEW YORK ( TheStreet) -- When studying cloud computing I feel like a kid again.Not always in a good way. Take applications, for instance. Please. The big cloud software outfits are either offering infrastructure like Amazon.Com ( AMZN), or building platforms like Red Hat ( RHT). An infrastructure is just capacity you rent. A platform just lets you write your own application, which is something of a one-off. This is the way computing was before IBM ( IBM) created its System 360 in the mid-1960s. The 360's big innovation was an operating system that let you write a program once and run it on multiple machines. No more fitting the machine to the software. This was a very big deal. The System 360 was followed by the rise of the mini-computer companies, like Digital Equipment and Data General, whose refrigerator-sized boxes didn't need special rooms but which (more important) ran standard software, applications you could just load and run. Today the leading "cloud application" company is Salesforce.com ( CRM), but as CIO Today noted in covering some of their latest announcements, they're offering applications only within their own cloud, just as IBM offered software only on its own mainframes. Google ( GOOG) is offering standard office applications, like word processing and spreadsheets, but, again, they only run within the Google cloud. A start-up called Snaplogic has just gotten $20 million to help companies integrate cloud applications with their on-premise solutions, notes TechCrunch. Connecting what you have with what you have in the cloud is going to be a big business next year for companies like Dell ( DELL) and IBM as well, writes TechTarget. The problem is that the biggest public clouds today are fundamentally incompatible with other clouds. You can't take a piece of software off an Amazon cloud and run it on a Google cloud, or on Rackspace's ( RAX) OpenStack cloud. This is the opportunity open source has been waiting for. Systems like OpenStack, RedHat's OpenFlow platform, or VMware's ( VMW) Cloud Foundry are designed to let you write one application that will run both on your private cloud and on a public cloud, or a selection of open clouds. Both Dell and Hewlett-Packard ( HPQ) are building clouds with OpenStack for just this reason, to create application compatibility between public and private clouds.