tried it for a few minutes, and got a few criticisms meant to be constructive (no pun intended)
first, is just a suggestion/opinion, the demo version, maybe saving disabled would be better than letting someone only make half a beat. There are alot of ultra-polished superawesome beatmaking programs out there, with very liberal demos and trial versions. there's even some really great free one's. you would probably be aiming for a more niche indie market, but still, you gotta make it so they have fun, and make something that sounds cool. A halting half beat is only frustrating to listen to, and no fun at all. same thing with no looping, you have to get them addicted to it. this would be the equivalent of having a racing game demo, where the car was limited to 20mph, and you weren't allowed to finish a lap. once again, just an opinion, and it's not like I've ever sold software before.
next, would be the ease of use. not sure why the choice the choice to have little squares above the rectangles with the "wav" file names with the abbreviated names. but the little squares seem like they should be right clickable, too. maybe a way to preview them in the dropdown list as well, perhaps right click again?.
the preview sounds in the bottom left are useful, but it seems like you should be able to right click them to automatically assign them to the last selected slot on the beat maker to the right, also even after realizing I couldn't do it, I kept trying to drag the files from that list onto the beats. if you need some help on how to make something from the listbox drag and droppable, I'd be glad to help. on the interface note as well, being able to hold the tempo change button to change the tempo continuously would be useful, and also, being able to click on the actual tempo number and type in a new tempo would also be good.
I couldn't pinpoint when it happens, but its definitely not all the time, but sometimes i think it rushes between the 16 and 17 beat and plays the 17th beat too early. after switching to several beats, and switching back it had righted itself.
I think it's cool that it gives help to noob beatboxers. in general, it seems like a nice little app, and I wanted to throw a quick beat together and post it, but all the demo limitations, as well as the interface issues made it a frustrating process.
the basis of a fun tool is there, though, and I think you should keep at it