(Version reviewed: Either the original or the first update. I reviewed this right around the time it was updated, so I'm unsure.)
Trapped in Time is a fun and novel CYOA game which operates not on a computer but on paper, either real paper if you print out the PDF file which comprises the game or on the virtual pages of the PDF itself. It is divided up into numbered paragraphs as per a Fighting Fantasy gamebook, and whenever you make a decision you will be told to turn to a particular paragraph. I played the game just by paging back and forth through the document in a PDF reader, a method which had the added convenience of enabling me to take notes by copying and pasting chunks of prose into a TextEdit document. Unless you have a very good memory you'll need notes to stay abreast of the game's trickery, and that trickery leads to an outcome I found strangely moving.
While Trapped in Time's prose has the clear, enthusiastic and kid-friendly style of one of the original Choose Your Own Adventure books, I'll point out that four-letter words and a bit of violence do make appearances later in the game. Ruling out kids who shouldn't be encountering four-letter words, I recommend the game to all and sundry.
Complete spoilers ahead.
In Trapped in Time you play a newly minted Chrononaut, a time travel test pilot, the best in Denmark, and you're about to enter the Copenhagen Institute of Chronology for your first time trip. After you step into the time machine, sparks fly and you find yourself back at the start of the day, standing outside the Copenhagen Institute of Chronology again and actually reading the same numbered paragraphs as before. The difference this time is that you've been informed that you can tell people about your strange experience by adding 30 to the number of the paragraph in which you first speak to them, and reading that paragraph instead. This is the first of a good number of such math-powered mechanisms for taking new actions you'll acquire during Trapped in Time, hence the need to take notes.
These addition / subtraction / multiplication tricks were used by the authors of various Fighting Fantasy game books throughout the 1980s. For instance in Phantoms of Fear (1987) if you saw an asterisk at the start of a paragraph, you could move into a dream state by adding a certain amount to the paragraph number. However, the Fighting Fantasy books were much larger than Trapped in Time and had many other mechanisms at work. Trapped exclusively uses the maths tricks, and uses them more than than any other individual gamebook has before. Of course, it's also fairly novel in using them in the service of a time traveller's loop.
The time travel concept and the overturning of staples of CYOA are played out on many levels here in a way that speaks to adults like myself who grew up on these gamebooks. The earlier stages of Trapped in Time treat you more like a child reader and occasionally invite you to write your name in the book. But as your time stream becomes more messed up and your character becomes more stressed, he starts swearing and opportunities for violence arise. The more exciting of the two endings to the game declares that your ability to travel in time is a form of cheating (I.E. reading paragraphs you weren't told to read) and that you really could have turned to any of the paragraphs at any time, and can do so now. You can use this power to find easter egg endings which are never referenced in the text of the main story.
I was mildly shocked to have a paper gamebook say directly to me: "You can cheat, and you've always had the power to cheat." Obviously I wasn't shocked because this was any kind of revelation, but because commercial gamebooks didn't acknowledge, let alone encourage, this extremely common practice. I felt like some grown-up had just told me something I'd always known but which nobody was allowed to talk about. This outcome cemented nostalgic feelings in me which Trapped in Time had already stirred, but they were just a pleasant bonus on top of what is an excellent gamebook in its own right.