Neutron is a vertically-scrolling shoot ’em up created by Sarah Jane Avory and first released for the Commodore 64 in 2019.
It was created for the 2019 RGCD C64 16KB cartridge game development competition, and is actually a re-coding of a game Sarah created in the 1980s but that went unreleased (because the publisher she was tied to at the time went out of business, before the game’s release), and was eventually lost (she regrettably threw away the disks with the source code after moving house years later).