So for an alternative to OF, I have to acquire Organize:Pro, a heavy duty tool meant for professional project management and control. Ironically, it is well designed, contains unique advanced features, and yet is a lot cheaper than OF. @Omnigroup: this should get your attention. OP is less flexible, but in terms of functionalities and UI you are being outclassed at a lower pricepoint.
I noticed a couple of quick downsides.
1. No user forum. I absolutely despise doing business with any software company that in the year 2013 does not have user forums. I don't want to be stuck writing support every time I have a question.
2. One of the things I love about OF is being able to assign a context not only to actions (which all the GTD programs do), but to projects themselves. Does not look like OP supports that.
3. It does not appear as though the user can easily select all projects or all contexts and progressively filter down as desired, as can be done with OF. A parent project must be selected. I suppose the user could use a workaround of creating one master project that holds all other projects, since it appears you can create a project tree with as many levels as desired.
Anyhow as always no product gets it perfect. I'll stick with OF, but Organize:pro is one of the most interesting products I've seen in a while.