I just had a fallout with KNotes 'losing' my few notes after an upgrade, and it was a major sweat to finally track down the notes saved in two Akonadi folders elsewhere. It got me thinking though about proper cross-platform syncing sticky notes (not note managers like Evernote, Google Keep, QOwnNotes). Some like Microsoft's Sticky notes don't 'stick' on Linux. I ma using QOwnNotes already for masses of text based notes which sync via my NextCloud.
There was a great solution like this called Cloud Sticky Notes that synced to Amazon Cloud but the site is now unavailable. Notezilla is halfway there for Windows and iOS and Android, but no Linux or MacOS.
So I have found two Java apps that are Windows, MacOS and Linux but no mobile clients, and neither do they actually handle concurrent multi-client syncing. GloboNotes includes the kitchen sync for features but is a database and is Freeware and not open source, whilst Pin 'Em Up is open source and XML format, but is very bare bones with no text formatting, and has had no updates for 7 years.
I'm looking for:
* Proper sticky notes on the desktop
* Works on Linux, MacOS and Windows (and bonus if mobile too)
* Open source but worst case freeware.
* Preferably stored in XML or plain text format for recovery
* Yes basic text formatting like bold, underline, indenting/bullet lists
So GloboNotes or Pin 'Em Up would fulfil the real basics probably for me, but am I missing some hidden gem out there?