Ask HN: Free/Open-Source Invoicing Software?

At the moment I can not afford to spend money on a lot of the great options out for invoicing and was wondering if the community knew of any free or open source options out there.

Some of the features I am looking for:

Input your business info, Input client info, Input project details and cost, Generate invoice PDF, Generate receipt PDF,

Bonus:

Ability to mark/track who had paid and outstanding balances.

How do your clients usually pay you?

I do freelancing on the side and would use Paypal with smaller clients, but now I'm getting larger clients and wanted to make it more professional. I started using a free app a while ago and then realized I can only have 6 free invoices which just ran out. It also doesn't have an option for reciepts, which I just got asked for for the first time.

Seems strange to me that you cannot afford the "great options" if you're getting bigger clients! QuickBooks costs $10/mo, and the competitors like FreshBooks are in the same range (~$12/mo). I use QB and am quite happy with it; worth every penny to me :)

I tried the free options for a long time and finally gave up and went with Freshbooks. I wish I had done it sooner because the expense tracking and reporting makes it a good buy. Frankly, it's not worth the effort of doing all that myself.

Their free plan supports invoices for one customer, so you can try it out easily. I'm on the undocumented $10/month plan for 5 customers but was on the $20/month for 25 customer plan for ~2 years.

(I have a regular job right now but have a few projects here and there that come up.)