I finally settled for this :
- - Text only notes.
- - MarkDown format (https://en.wikipedia.org/wiki/Markdown).
- - Work PC : ResophNotes (http://www.resoph.com)
- - Home Mac : nvAlt (http://brettterpstra.com/projects/nvalt/)
- - iPhone : SimpleNote (http://simplenote.com/)
- - And all notes synchronized with SimpleNote
Yes, it is not an open source solution (even if some parts may be open source); but I am not dependant on any company or its format. If SimpleNote goes bankrupt or starts behaving evil, I can switch to DropBox for file sync (or any other similar service).
It is not as sexy as Evernote, but I am 100% sure that I will be able to access my notes in 20 years.
BTW : I first typed this in MarkDown...