The problem with landing pages like this is that they capture interest in the concept, not your execution of it. At a high level sure, being able to produce documentation faster sounds good but how does it work? What will we have to give up [money, branding, the url]? Perhaps the freemium model would work, perhaps a very low cost for a limited account... Staying lean in what you build is great but don't mix up a minimal product with a minimal effort -- to get a good read you need to shown enough "skin".
And of course the difficulty you'll face is proving value. Even if what you build is amazing it's still competing with free and unbranded rather than some pricey competitor thus you have to convince people there's enough time suck to warrant whatever cost / ads / marketing you put into the mix.
Ted, thanks for your detailed reply. I totally understand you.
Let me explain the "idea" a little bit more detailed.
I have developed some other softwares and online services and one of the biggest challenge I've faced is writing user guides/API docs for my softwares. Table of contents, indexing, search, rating, discussions and all other "parts" of this eco-system is challenging. I ended up using ZenDesk to power-up my knowledgebase/user guides but it's not user friendly. I am limited.
I decided to build my own "user guide" builder. It will be dead simple. There will be several "cool" user guide/API doc templates, it will be re-brandable and you will be able to point your own domain (ex: help.yourdomain.com) to the system. You will set your page templates and then start building the documentation. My service will handle the rest for you. ToC generation, index, search, rating, comments, statistics, integration to ZendDesk, Assistly, etc.
In exchange, users of my service will pay a reasonable monthly fee. I don't like free plans, therefore my monthly plan have a no-credit-card required 14-day trial period. Maybe I can add a very limited free plan with a badge at the bottom of user guides.
What I'm curious is whether this idea will work and I can find 10 paying customers...
I will follow Lean Start-up methodology on this project to lower my costs and quit early if it's not going to work anytime soon.