There are 3 repositories under retrobat topic.
Compilation of BIOSes for various emulation platforms
RetroBat is the best way to play your ROMs collection on Windows !
A theme inspired by the PlayStation 3/4 interface, featuring custom avatars, usernames, retroachievements compatibility and much more for Batocera, RetroBat, and EmuElec frontends. Also available on the official themes download list
Retrofix - A theme for Batocera and RetroBat 5.25+.
Projects from what was MrOverlay.org
ArcadeFlashWeb is a program to play Flash Games (SWF), on Windows 7, 8, 8.1 and 10, without installing Flash Player (works despite the end of Flash). Versions : command line and GUI (perfect for Arcade Cabinet).
A toolbox for EmulationStation gamelist.xml romsets.