I like invoiceninja. No connection, just a happy user. It's been going a few years, open source, free (paid option for no branding), payment gateways and so f

I like invoiceninja. No connection, just a happy user. It's been going a few years, open source, free (paid option for no branding), payment gateways and so far has been reliable. You can also set scheduled recurring invoices, even on the free tier.