[Jefro118]

An ebook will likely be much closer to passive income than a SaaS product. Neither are passive though - if you want to have a consistent stream of income you will have to continue doing work. And you will certainly have to do a fair amount of work to get it off the ground (this includes marketing and/or sales, not just making).

For SaaS, having a product that you can put on third-party marketplace, e.g. Shopify apps, GitHub apps, etc. might be your best shot at reducing ongoing work since the marketplace itself will do some of the marketing for you. You still have to do lots of work though.

Mobile or web based game will likely take a lot of work and return very little.

Aggregating useful content and selling access to it is one relatively quick way to go. E.g. there are bunch of people who have just aggregated contact info of press or VCs and then sold access to it. This will take a fair bit of work to aggregate all the info but it's still relatively quick (certainly compared to SaaS) and probably won't require much ongoing customer support given how simple the end product would be.

Ultimately if you are determined to find something which is "passive" you are more likely then not going to fail. By all means think about how you can compress the time and effort required and reduce the amount of ongoing labour by you, but starting from "I want passive income" isn't going to work.

[ghaff]

I'm not sure I'd ever recommend an ebook as a good passive income method. There are good reasons to write a book, including establishing credibility that leads to more revenue for consulting etc. But you're probably not going to make a lot of money from it.

[Jefro118]

I was referring more to relative passivity rather than income potential, but I haven't written one myself and I'm not too sure whether it's worth pursuing at all if your goal is money so I'll take your word for it.