Software as a service (SaaS) is the first part of the cloud stack for those enterprises who prefer a buffet approach to IT purchases. If you only need to buy a CRM module, then you don't need the whole ERP solution. Salesforce figured this out first, then Adobe jumped in, and Microsoft eventually figured it out. Oracle is just now figuring it out.
Platform as a service (PaaS) is the second part of the cloud stack for the operating system, databases, and programming languages that are the exclusive provenance of nerds. In between configuring PaaS for clients, nerds can be seen running their video games in the background.
Infrastructure as a service (IaaS) is the third and final part of the cloud stack. The data center's hardware of servers, racks, network connections, and other physical stuff become the rented or shared assets an enterprise no longer needs to own. IaaS is the nerd version of the sharing economy trend. Outsourced data centers will see extreme growth as Big Data crowds into the increasingly cramped space of Moore's Law.
Information Technology as a service (ITaaS) turns the IT department from a cost center into a profit center. That is harder than it sounds. It doesn't just integrate the three cloud stacks above. It's supposed to use a bunch of best practices from a proprietary library. I hope CIOs read about Cloudonomics before they announce an ITaaS strategy. Lots of IT people aren't natural sales people, so any "products" they create must find a market outside the enterprise. This requires a huge reorientation in how IT perceives its customers; the buyers aren't all inside the firm anymore.
Desktop as a service (DaaS) is now called virtualization. It makes your desktop apps look like they run from your local PC, but they really run from the cloud all along. Desktop PCs are losing market share and they may evolve into very specialized local workstations for a cloud presence at some big piece of physical plant.
Mobile Backend as a service (MBaaS, or just BaaS without the mobile) sounds like it involves a private dance at a gentlemen's club. It actually leverages the data supply chain of SDKs and APIs to put the cloud's power onto a mobile device. I'd use an app for purchasing dances in the champagne room if it meant I could see some hot chick's mobile back end.
Data as a service (another DaaS) is just the raw data with no applications to process it. Big Data and Small Data need someplace to go, and those enterprises still wedded to on-premise software use DaaS just to move the flows to their client desktops. It's too bad this data DaaS shares the same acronym as the desktop DaaS above. These things get confusing for anyone who's not a genius like me.
Database as a service (DBaaS) sounds like an interim solution for enterprises that need more than DaaS but aren't ready for a fully mature cloud deployment. The outsourced database uses management protocols that may or may not include virtual machines. I suspect DBaaS will evolve into a teaser marketing ploy that cloud providers use to encourage late adopters to gradually enter the cloud stack.
Identity and policy management as a service (IPMaaS) sometimes goes by "access management," according to the results of my Google search. Enterprises who need to manage policies for both internal users (BYOD) and external users (privacy, regulatory compliance) will need more of this service as their product lines grow in complexity. Proliferating devices inside the enterprise means the IT folks need to stay on top of single sign-on and universal access.
Network as a service (NaaS) is a model for flexing the three cloud layers as their traffic patterns change. It sounds great in a marketing pitch. Making it work means having analytics on the back end to predict demand for nodes in real time. Accurate predictions need tons of input from domain experts who understand an enterprise's seasonality, geographic presence, and other things unique to its markets.
Everything as a service (XaaS) is all of the above combined in one package, as far as I can figure. It will probably be the preferred solution for noobs who haven't yet figured out their enterprise needs, or naive gladhanders who think going whole hog into the cloud without a total cost of ownership (TCO) analysis will make them cool. It will also be the preferred fallback marketing ploy for cloud sector providers who target late adopters.
Baloney as a service (BaaS) is my own term for fly-by-night cloud operators pushing vaporware and empty promises. There will be plenty of these people running around as the less tech-savvy sectors of advanced economies migrate to the cloud. There's already a lot of baloney thanks to multiple startups promising miraculous cloud integration with social networks and localization services. Most of that ground is already covered. First-mover advantage came and went. The first-movers who won are massively overvalued after their high-profile IPOs. The stragglers are about to be vaporized as they wildly spend through their cash.
I just explained everything there is to know about the cloud in this listicle. Okay, you got me, maybe not everything, but enough to impress dumb (but hot) chicks at a bar. A finance person like yours truly can only scratch the surface of the cloud.