NOT gui, but worth a squint: UPenn.edu 's UNISON

USES rsync (dependency; also ssh)

IT WORKS no matter which way you've installed your Linux host server.

AS WITH rsync (good example, Trevor), BEWARE "direction" .. "who's the boss" ..

TEST: definitely set up HERE://~/exampleDir/ _ and There://~exampleDir/ with files like, say: OrangeFile,BlueFile,GreenFile in SOURCEdir (Here) and YellowFile, RedFile in DESTINATIONdir (There)

and LEARN that a) you've either config'd "direction" properly, .. or .. b) you've clobbered DESTINATION, 'coz it's pushing wrongway.

Seeing is believing.

"ALLOWING" unique items to survive sync, at destination, which do NOT exist at source, is tricky.

Somewhat eased configs, telling Unison how to behave, after initial setup/test session. Then we can (sudo) edit its config file; /root/.unison/default.prf

ADVANTAGE rsync: Cordes' example here, is just as strong a starting point (and rather more concise). Please note that files in your system with extended file attributes will come across better with rsync.

ADVANTAGE Unison: it is platform independent. So, you can dodge dissimilar syntax/vagaries where rsync talks between dissimilar platforms. e.g: WinX .. to Linux .. Or .. OSX .. to WinX .. Or .. Linux to .. etc Here is a Unison tutorial: https://www.howtoforge.com/tutorial/unison-file-sync-between-two-servers-on-...

That tutorial establishes an ssh encrypted connection. If one of your hosts is anaemic (slow CPU) stay with rsync, and without ssh/encryption.

Re: TEXT EDITING of config files - "vi" is always present on a unix system - you want to learn it, but not in a hurry. PRACTICE is NECESSARY "nano" (I believe) is present in default Ubuntu/Mint install - less cryptic, less landmine kbrd

Note: Tutorial installs nano. IN EITHER CASE - practice text editing from Command Line Interface "CLI"

REMEMBER the folder/path/folder/path delimiter is 'slash' .. NOT backslash

ASIDE: One would vote we never again refer to 'slash' as 'forward slash', to avoid needling from the greybeards

THESE UPenn people who set up Unison, I believe, did it for simplicity (not just xPlatform). YMMV.

DISADVANTAGE UNISON: THESE OXFORD pointyheads are NO LONGER ENAMORED with Unison, and give very good examples for obscurities of rsync; e.g: using wildcard star/asterisk/"*" will miss .dotFiles https://www2.physics.ox.ac.uk/it-services/how-to-use-rsync

John D