[amanvir_sangha]

It saves a lot of developer time, you would just have to write the docs in markdown, not have to worry about the layout, hosting or building another app just to manage your docs. IMO it provides a lot of value for money. You could always just use the free plan and then upgrade later. With markdown files, you wouldn't really get locked into the platform.

[phaer]

As far as I see, Readme.io has additional features but everything you've listed is available for free on readthedocs.org, built on Sphinx which is free software.

[prottmann]

Why should they not coexist? Some want it for free and some want to pay for e.g. support or additional features.

Last time i watch at RTD it was a plain .md project import from e.g. GitHub only to show a plain documentation.

In Readme.io you can edit/write your docs, have blog function and an integrated discussion plattform (for support your users). If you not need this features, you can use RTD or directly sphinx.