What is an open door novel?

English is not my first language so please take care of me and if you find mistakes in it tell me I fix it as soon as possible. Max Winchester died due to an "accident" while reading the novel after his death he meet God who allowed him to travel through and do whatever he think best but on condition to make Protagonist's life miserable. He also gives him the strongest system [Netori system] that help him steal Protagonists Woman, Chances, Luck, etc Why does God want to make that Protagonist's life miserable? And why [Netori system] given to the max let's find out. (English will get better after chapter 38.) I don't own a book cover, I find it online, If creator wants me to change it just message me, I will remove it.

"Legend had it that in the deepest part of the oldest galaxy, there was a door as red as blood and fire. Legends and myths, darkness and light, countless stories passed through this old door. The Door of Constellation that overlooked everything would warn the sky and earth, sending darkness back to where it belonged."

2nd year of High School, Yoona. Her mother had left the world early and left her and her father by themselves. She relieves her stress caused by her troublesome father and schoolwork through watching Idols. But one day, her father announces that he will be getting remarried! And her new stepmother has a son? Yoona suddenly gets a new brother...

Will appear in another novel with the same name within the next month or so as I properly rework it. Curse my inability to leave things unfinished.

Uriel has lived a difficult life. At the age of seven, his father, whom he most admired, suddenly abandoned him. He faced endless taunting and aggression from his schoolmates, until... An unexpected event occurred, which led him to a mysterious and desolate place. A cruel place, where you can be betrayed by the one you trust the most at any moment; where with every passing second, billions of people die; where powerful beasts and ruthless demons run wild. After living a ruthless life in that place for ten years, Uriel returns to his original world - Earth! However, on the very day of his return, he ends up going to another mysterious place with his father's arrangements. What he did not - or perhaps - expect, was that that place was the location of his favorite webtoon - Tower of God! And the surprises were never-ending. 'Urek Mazino?!' Upon entering the Tower, one of the first people he meets is the famous Urek Mazino! *A lot of bloody scenes, really a lot. The MC will not pity anyone, there will be torture, massacre, betrayal, killings, and so on. Discord: https://discord.gg/t5vzVduRdY

Mike transmigrated into a world with swords and magic. Immediately, he acquired a fitness gym. He was invincible in the gym. The stronger he grew, the size of the area in which he was invincible grew larger too. However, the prerequisite of him becoming stronger was to have more people working out in his gym. Mike came up with all sorts of ways to gradually increase the visitors coming to his gym. The people in this alternate world realized that compared to other gyms, the result of their exercise was more prominent when they worked out in Mike’s gym. On the other hand, Mike also realized that he gained something every time someone worked out in his gym. [Ding! Someone is training their muscles using the machines. Strength +1] [Ding! Someone is running on the treadmill. Speed +1] [Ding! Someone is doing yoga. Tenacity +1] As more and more people worked out in his gym, Mike was slowly on his path of becoming invincible!