It has swipe up/down + double tap gestures. You can also customise the home and back buttons.

It has swipe typing plus a lot of other new features/theme customisation that openboard didn’t have.

PhotoDemon is close to what you’re asking for. It has the basic functionality the average user needs yet is still lightweight and fast to start.

They have different usage scenarios.

LocalSend is for the occasional sending of files/folders from A to B or B to A (One direction only).

Syncthing’s primary usage is for keeping the exact same copies of files on A and B automatically.