In 2017 William Kalfelz started with some cheap 7-segment / button boards from eBay and an ATMega to implement a MIDI sequencer. See this video:
Later Gert Borovčak built a version as well and helped improving the firmware with William. He even manually desoldered the 7-segment elements and buttons of the eBay board and soldered a custom version on perf board, see this video of a short demo performance:
Then Gert asked Frank Buss to develop a professional PCB for it, maybe even to sell it later commercially. But everything will remain open source and open source hardware.