Preface: I realize the following is asking for tinfoil-hat type security, but I'm really curious for answers to my questions -- not suggestions to enable two-factor logons on gmail, etc. and call it a day. Please humor me.
The basic issue is this: I use multiple computers, and really like the convenience of proprietary cross computer sharing services (gmail for email, chrome sync for passwords and bookmarks, dropbox for files, etc.). However, my recent experience with Syncthing (an open-source file synchronization program) has been very positive, and it has made me wonder if I can somehow sync email, passwords, etc. that are stored only on my own computers rather than in "the cloud".
Is there a good way to avoid "the cloud" and still have everything sync smoothly while allowing for easy-to-use applications?
For example, I use KDE and could share my kwallet file, kmail email folder, etc. using syncthing.
However I'm concerned that this could lead to synchronization conflicts. E.g. having several computers all running an email client simultaneously could step on each others toes. The client on one computer downloads an email which is synced around the same time that the client on another computer downloads the same email. This could create some type of conflict. Or maybe the client on one computer saves the email in a file with a different filename than the email client on the other computer, meaning that all my emails are duplicated.
I'm sure there are other issues.
Do you have any thoughts on how to get around these issues? I realize that I'm asking for a lot, but someone had to ask.