Selfhosted

FX File Explorer has a local web-access feature. Start it on your phone and access via local IP, then just turn it off when you're done.

Don't use on public wifi, it's http-only.

For more manual stuff; Ssh and X-Plore File Explorer.

Internal, sd card, ssh, ftp(s), google drive, dropbox, and a bunch of other cloud providers; treats it all like one big file system that I can casually copy/move files between.

For just syncing files between folders: FolderSync. The 'downloads' folder on my phone is setup as a 2-way sync with a folder on my server. Drop a file in either side, click sync, file is in both places. I use this to keep most of the files on my phone backed up, not just syncing the download folder.

I use QuickDAV and OwlFiles.

I use Cx file explorer and mount my PC via sshfs in there. It's closed source but it supports a whole bunch of protocols including samba, ftp and webdav. And it can launch a webserver on your phone to offer the phone's files. But sshfs is the most convenient for me.

And for links and other small texts I use either KDEConnect's copy and paste sync or just send myself the text in Signal.

I use pairdrop. I don't personally self host it, but that option is available. It's better suited to more one-off situations, as there's no history kept anywhere.

Selfhost: https://github.com/schlagmichdoch/pairdrop

Open instance: pairdrop.net

I've tried LocalSend for this, but I usually end up using more reliable ways like Syncthing (not instantly transfered, but at a decent speed) or sending myself the file on Element for Matrix (as good as instantaneous).

Taildrop works relatively well for most all circumstances. Only thing is you gotta use trayscale or cli currently for sending files from a Linux/bsd machine. I don’t know if opened has a port for trayscale but it definitely has a port of tailscale.

I'd use anything else that is based on rsync over Syncthing

I often spin up a quick python http server. Just go to the folder which has the files you want to transfer and run the following command: python3 -m http.server. This will server the folder content Serving HTTP on 0.0.0.0 port 8000 (http://0.0.0.0:8000/) .... On your phone you can then browse to http://PC_IP:8000 and download what you want/need.

Signal

My solution is scp with termux. I can't suggest any better alternative.

Does your PC have Bluetooth? Definitely quick and sort of self hosted.

I use SyncMe which synchronizes smb shares to your phone. It's great once you have it set up, but it does take a little setup. Gotta have shares and whatnot.

You got some good replies and I personally am enamored by LocalSend, it is worth checking it out.

However, there is a simple way if a) you use whatsapp and b) the devices involved have access to whatsapp.
This involves not just sending files but you can send text and whatever whatsapp supports and you'll have a history of these chats should you need to have them later again. Probably possible with other platforms but I use whatsapp so that is what I setup for information transfer to myself.
The thing you want to do is create a chat group, add a friend for a very brief moment, remove said friend again after they accepted, enjoy your private group where you can dump any and all info into and pick up from wherever you have whatsapp available. The trick is to add a friend for a couple of seconds. If you create a group you are automatically in it but you cannot use it until you add someone else, then it becomes active and use-able. The fact that you end up alone in that group does not make it unavailable again. Weird but it works.

I didn't see it mentioned yet, so I'll throw warpinator in the ring.

Clients are available for Linux, Windows, Android: https://warpinator.com/

KDE Connect as another uas suggested.

Only buggy issue I have is that I use a VPN on my phone to access my local network when away from home. I have the VPN set up with Hairpinning so I don't have to disconnect from the VPN while at home which occasionally causes issues on my steam deck as the version of KDE Connect on the steam deck does not appear to have an easy way to connect to device via IP. On my desktop and laptop I run Pop!_OS and use GS Connect which gives me an option to connect to device via IP so I have less issues with my phone just randomly not appearing on those computers.

For links, I use Pocket (you can use Wallabag, but I find the interface not efficient at all). For files, you can sync a folder with syncthing (but you only switch it on when you want a quick sync, otherwise keep it off for battery). If you just want to put some file on your phone, install FTP server (free) from F-droid and switch it on when you need it (there's even an optional switch on quick actions). Use Filezilla or any file browser (if on Linux) to exchange your files. Remember to switch the server off once finished, because FTP is not a secure protocol.

Android -> other I often use Share via HTTP.

https://github.com/marcosdiez/shareviahttp

This sounds great. Thanks.

rsync -avr --progress in termux or a file explorer app built on top of scp or rsync. It doesn't work like your use-case, but I've been happy with it.

I'm using a selfhosted pastebin (microbin) as sometimes I want to transfer text, other files... It's very efficient and in my instance it's using 13MB of RAM, which is fairly lightweight for modern standards

email.