I use WePay's invoices for a non-profit that I help run. While they weren't perfect (what is?) they did the job and let me focus on other things. I'm now on the lookout for a simple invoicing platform that supports single and multi-payment invoices and some basic branding capabilities. I might even look at building something on their API or Stripe (would lean towards Stripe as I've used them before but IIRC their fees are a touch higher).

Sad to see these services go, but I can imagine that the support burden of a consumer-facing service is something they'll be glad to be rid of if nothing else.