Articulate 360 now has a web-based tool called RISE that I have been exploring when I have a few extra minutes. I am crazy about this tool because it is simple, easy to use and the product looks great on mobile devices. It is called RISE and although it does not have all the interactions that Storyline has, the result is still effective.
Here is an example that another designer, Valorie Engholm, put together that shows all the features.
The only issue I have found is when entering text, the formatting can get a little funky. When that happens I just copy the text into Notepad and then recopy it back in.