Comment by WilliamMayor

I've built https://billabl.co with this idea in mind. It's early days and I'm just hacking on it as a side project. I use the event title for the project name, or sometimes the client name (depending on how busy I am with that client, or how detailed my invoices need to be). Sometimes I'll create a separate calendar just for one client. So far it connects to Google calendars only.