There are two different cases for the Windows store :
-Publishing ‘Windows Store apps’ with the “Metro” RT interface : this can be done as an individual for very little. Because applications use a different framework, Visual Studio must be used, and the learning curve can be steep. Especially since just as Objective C, this environment is made by autist nerds. I have overcome the hurdles and got 5 apps online.
- Listing desktop apps, which can be developed in Xojo. This requires a business account indeed. And signing the apps with a $499 a year Verisign certificate, plus your own electronic sales web site, as the Windows Store does not take payments for desktop apps. Moreover, desktop apps are a minute minority in the total offering. Probably the result of all these impediments, as well as the fact that the Windows Store app works only with Windows 8 and 8.1. A rather idiotic move when the real strength of Microsoft Windows resides in the huge installed base, from XP on.
All and all, the Windows store showed for my apps about one fifth of the current Mac App Store potential. I am glad I did not invest into the Verisign cr@p.
Building for the Mac App Store is pretty straightforward, and has been largely documented in this forum, where numerous members have apps there. I use App Wrapper Mini from Ohanaware to package my apps, and had very little worries.
I believe the Mac App Store is where there are the most opportunities. Strangely enough, the PC market would seem overwhelmingly larger, but its structure is less conducive to business : most apps are offered for free or shareware, and customers do not seem to quite understand the need to pay for their programs. The Windows Store is to my knowledge the only serious place of shopping, and their insistance to force users to Windows 8 defeats desktop sales.
I have been investigating http://allmyapps.com/ as a possible venue for Windows business. Unfortunately, it offers only free apps, so the trick is probably to create a limited or nagware version in the hope that some users will eventually buy the pro issue, with some in app or web site purchase solution. Although I have been a member of Association of Software Professionals (formerly Association of Shareware Professionals) for a while, I have very little information about these download platforms in terms of transformation rate. In the standard shareware business, one or two sales per a hundred downloads is considered a huge success. I have personally observed much, much less. So the amount of work to turn new software seem overwhelming.
These days I tend to develop for Mac only. I had enough of the cheap Windows crowd.
I am not aware of a Linux store. Given the installed base (1-2% according to most sources), I would be extremely surprised that customers used to freeware would put their money in any pay-for apps if a store existed.
Developing for Android cannot be done with Xojo, and require using the free tools available from Google, or LiveCode, Basic4Android or several other development tools. As far as I know, placing an app in the Play Store is not difficult for an individual. From what I have been told, though, unless you are Candy Crush, sales are not as vivid as the MAS, and prices are low.