Hi,
Is there any app for Android which would allow to create Grav posts from smartphones?
The scenario I’m thinking about is to snap a photo (or select photos from the gallery) and have a way to create a new post with a “one click”.
hi @Bronek ,
welcome to the Grav community 
.
as for your question, no, there is IMHO no Android (nor IOS) app for Grav Post/Page creation.
if this is just to create blog posts, with always the same template (e.g. item.html.twig) I think it would not be too hard to create a little web app with ajax (javascript frontend, PHP backend) that does the job.
otherwise, why not just use the Grav Admin ?
that is, at least, responsive and thus can be operated even with a phone, though not exactly suited to that use case.