I agree, the UI is not really simple, but it is very functional. regarding the docker setup it also took me a couple of tries, but I succeeded in the end.
I have been researching this subject for a while as well and eventually settled on using Odoo with the full accounting features. It's more than just accounting but it works quite well and it's free. Can be run as a single python docker container.
Some things are, but the core functionality is easily extended through modules and you can find a lot of sites with them. Some of the best modules are going to cost you some money but it’s worth it.
That being said Odoo is overkill if you just need to send an invoice. Odoo is perfect for running a business though. It can and will do EVERYTHING and then some.
I know people who run their entire businesses on it. Website, HR, inventory, time clocks, billing, etc etc. it scales really well too. Largest business I know using it has 100s of employees. They even have a paid developer on staff that writes and maintains custom modules for them. Smallest business I know of using it has 5 employees, including the owners.
Hmm I end up managed to install invoice ninja with dockerfile repo I used wrong env file and it was making error. For plus I like apps both for iOS and Windows :)
My friend and I have been building just such a program for a while now.
We are both self employed software devs and we didn't have a clean way of tracking time, so we started building something that just did that at first, but it's evolved a lot since then.
However, it's still very much in development so customisation is limited, but the core stuff all works.
Now granted, it doesn't use docker, it's just a stand alone program and currently doesn't have cloud support (we are working on it), but I can absolutely send you a copy if you wanna try it out.
I've had good luck with https://akaunting.com/ but I did pay $50 for their estimate module. I think it'll do what your looking for in the free version though.
Well, openERP or openbravo were what I would have recommended ten years ago, but due to their commercialization aren't really relevant any longer. If I personally was setting this up for myself I would probably use redmine and a plugin that gives redmine the invoice functionality. However I wouldn't call it simple for a first timer to pull off, but if redmine is mastered you will find very extensible and customizable to any particular project's needs.