Ask HN: Can it become a startup or be sold?

I work for a digital agency that build sites and online campaigns. The main product there is a CMS, it is done in Flex and PHP. This app works but has some problems and they really want to move forward and leave Flex behind. Thinking about that and how it is done actually, i build a new app using standard web technologies (HTML, CSS, Javascript) at home and free hours. The content and layout of the pages is edited in place, i really like the results and have some cool ideas for it. Now i'v been thinking what should i do, i thought about 1) Try to sell then this app; 2) Make a startup from it; 3) Give it to then for some kind of better promotion because they offered one last friday if i become maintainer of the current app. So what is the right or best thing to do? Some advices?