It's a 12k equity-free grant, it lasts for 8 weeks, you can do it remotely, and it's primarily meant for idea and prototype-stage companies. No dinners and no formal Demo Day, but there will be kickoff and end events in Mountain View where teams will present to the YC community. We'll fly out remote teams for those.
Can my company join, aiming to finish our flagship product?
My company released lots of products, all of them had critical acclaim and high user reviews, but we ran out of money before releasing our main product, and we never had marketing money, so our sales are nowhere interesting.
I am wondering if you consider this early enough or not. (we had no investment beside from extra money from the original founders).
It sounds like you might be doing a company re-launch from the ground up? If that's the case, definitely apply for YCF.
If you still have successful ancillary products and just want to develop your flagship product with YC's help, consider applying to YC W16. Applications for that will open up in August.