I have many devices, and sometimes, I just want to transfer a single file without having to add a device to the list of known devices. This is similar to how Airdrop works.
If user enables this feature on device A, then sending a file from another device B should prompt A that B is sending a file and A can either accept or reject. If accepted, then it goes to a directory A designates (E.g: ~/DropSync).
This is not what syncthing is or does. What you are after is some different application. I’m certain there are airdrop alternatives out there.
I have a mobile sync folder setup on all my mobile devices and my laptop and nas. It’s usually empty. When I want to transfer to another device I just copy into the folder.
On the other device I just move the files out. Very quick. Very easy. Each file is transferred to all the devices but I don’t care. It’s just as quickly removed from all when I move it out on the device I was looking for it on.
One time setup and completely automatic. No accepting or having to specify where to place the new file (aside from just using the OS tools to move it where you want it.)
Very easy.
Neither option requires you to install any software. Similar to Airdrop. Only it’s called Sharedrop!
Both computers must be on the same network for this to work. Simply open any browser to that site from both computers. Select a file and it will transfer.
Hope this is useful.
I was thinking the same thing. Found localsend. Looks like it will do what I need.
Seems peer2server to me. Did not connect any second phone and clicked on “upload file” . Had 400kb/s outgoing, without a partner I guess my file hit the cloud instead so they can see my data. 
Yah, I gave up on that site. I also use localsend.
In the case that localsend doesn’t work I use send-anywhere. That works every time and you have to recognize and acknowledge a PIN code to verify end to end encryption. No software required but it is available.
Localsend is exactly what its name is it only works on one subnet it’s difficult to get it to work across subnets.
I prefer pairdrop 
I also keep it in my bag of tricks only for myself I prefer send anywhere because I can have an account which is free and send files across networks and through the internet to anywhere in the world. They even give you free cloud storage so you can send files to devices that aren’t even online at the moment. I can have one laptop running and send files to another that’s turned off and then swap laptops around and the file is ready to come down to the second laptop. Can’t do that with any of the browser apps.
It’s always good to have more than one option available when you’re trying to send a file to an unlike device impromptu.
Aside from desktops and laptops I have virtual machines running with a nat IP address. I want to be able to send a picture or file to one device from another easily no matter what network it’s on. I know you can enter a room with the other software but it’s just more difficult than if you have the actual software installed and logged in it’s very simple.
Localsend can act as a temporary web server and hand a QR code out to people who want to download a file from the phone so that’s a good thing to keep in mind also. Pretty helpful and gatherings.
I love tools and gadgets. I just found and installed software that runs on all three platforms Windows Mac and Linux and lets you create a second display virtually on any other device you own on your network that has a web browser on it no matter what operating system is running it can be a TV on the wall.