You know how some people attach several montiors to one PC? I don't. I just have several PCs. But then I want copy-paste to work transparently (as transparently as possible). For several years I used blitz to copy clipboard. It works well enough, but once you have 3 computers, it gets somewhat cumbersome to type the hostname. Also, it always bothered me how it rides ssh authentication. I wanted something independent from ssh.
Behold blitz2. Instead of passing the clipboard to the host where it's needed directly, the clipboard is uploaded to an HTTP server. Seems more complex at first, but it's actually much better, because previously the PC where you copy had to authenticate to the PC where you paste. Now the authentication is symmetric. So, all clients are configured exactly the same, and all can upload and download the clipboard no matter who trusts what ssh keys.