Stuart 
I asked HMRC what open source software there was for "Making Tax Digital". Their answer: use their software-finding tool. I'd asked them the question because their tool doesn't make that information available.
Does such a thing exist?
Stevie West@slowe UK Govt does provide free tax/payroll software for small businesses operating PAYE with under 10 employees. It’s called Basic PAYE Tools, available for Linux, MacOS and Windows. I’ve used it for many years and it does the job nicely. Baffles me that they couldn’t roll out something similar for the self-employed.