HTML would be a third alternative, yes. However historically it has been less stable in its definition, and also less stable in round-trip editing by a WYSIWYG editor - it has never been been an aim for HTML to be friendly to editing at that level. In contrast there are several editors which handle RTF without disrupting it for other editors. I use TextEdit (on the Mac), but of course it it is a common word processor format. RTFD is far less well supported, but I don't normally need images. I'm not familiar with any WYSIWYG editors for HTML which represent embedded images as though they were part of the same file.
> The main idea here is that I don't want to know any syntax like RTF
Nor do I. What I want is a file format which is long-term viable, and which I can edit in a WYSIWYG editor. The underlying file format being text-based useful as a recovery mechanism if RTF ever becomes unsupported, but it's not intended that one would edit it manually
> , nor I want to use any tools.
While I do not want to edit a file format manually.