Looks like a great tool. Thanks for sharing. Might consider using it if I start freelancing more, as I much prefer to support other small creators than big corporate software.
I started the project a while ago. My stack is Node.js with express + postgresql + redis + s3 + sqs + puppeteer (rendering html invoices/quotes/reports to pdf) for the back. The front is a browserify app with few modules: mainly D3 for the graph (https://momo.coach/blog/tech-stack/index.html)
Also the cat is nice.
Edit: Care to share your stack?