When I was preparing to the PSM I Assessment, I used the open Scrum.org quizzes which are pretty good. They contain questions that could be asked in the real assessment and have explanations. However, they have a couple of flaws. There is a small amount of questions and the questions are too simple.
Pretty soon I learned all the open questions, but I understood It is not enough. I started looking for other Scrum quizzes to prepare better, but did not find anything useful. One open quiz contained just 15 questions. Several others were not free and costed several tens of dollars.
I read the Scrum Guide many times, read other books and articles. Finally I passed the PSM I and PSPO I certifications, but I could prepare much faster if I had a good quiz that is based on the Scrum Guide and has enough amount of questions.
So, I decided creating my own PSM I mock quiz that is very similar to the real PSM I assessment. All the questions I prepared myself reading the Scrum Guide and related articles. The quiz is accessible in two flavors.
The Learning Mode is similar to the open assessments, but contains 80 questions. You could check the answer for each question and leave the quiz any time. This mode is good for preparation. After passing the quiz several times you could try the other mode.
The Real Mode is similar to the real PSM I Assessment. There are 80 questions (the same as in the Learning Mode) and 60 minutes to answer them. No prompts, no answer checking. If you score about 100%, you could pass the real PSM I Assessment with high probability.
If you are looking for other hints about passing PSM I Assessment, check my previous post.
Do not miss the chance to prepare well and Good Luck!