Borderless Gaming - Borderless Gaming v1.0.0 is Here - "A year ago we told you we were rewriting everything from scratch. Today, we're shipping something completely new."

Linux specific: XFCE has window manager tweak settings (in accessibility tab) that makes any maximized window effectively borderless (combined with auto-hide panel, of course).

Games are weird though so the ones that are fixed at native-res when windowed (NO maximize) don't benefit from that unfortunately. I personally have an ultra-minimal window theme that reduces that issue (it's only 12px off the top if you don't move it up). EDIT: I think Smallscreen is the smallest default window theme, though the sides and bottom of the window are non-0 so that adds difficulty to placement.