The Ren'Py Visual Novel Engine

The Ren'Py Visual Novel Engine
renpy.org

Interesting read/play, but not for everyone.

- It has all the basic featured you'd expect, ranging from proper backlogs, to key bindings, and much more. You'd be shocked how many VN developers think that they can just pop out an VN engine themselves, and end up producing something that lacks even basic features.

- It is performant. You'd be surprised how poorly many VN engines run really poorly. Fast-forwarding past already-read text is often capped at a surprisingly slow rate, with your CPU pegged at 100%, due to how inefficient many engines are

- It is easily moddable, as you just need to plop a (pseudo-)python script into the game folder, so you can easily tweak or turn off annoying bits of UI

A number of localization companies have also ported (typically older) Japanese titles to Ren'py, instead of having to struggle with poor to non-existent support for non-Japanese systems in the original engine, as well as extremely expensive engine licenses, and just straight up poorly written bespoke engines. Examples of companies having done this includes JAST USA, FAKKU, MangaGamer, and (IIRC) Sekai Project/Denpasoft. In other words, the heavy hitters of VN localization.

The other main contender for best VN engine (in my mind) is the KiriKiri engine, which I believe is also open source, but which lacks the large, English-speaking community that Ren'py has built.

Despite that, Ren'py does have a bit of a poor reputation in the older VN reading community, more specifically among readers who mainly read localized, Japanese VNs, due to its association with low-budget, originally English visual novels. Typically the same people have only heard of DDLC and Katawa Shoujo, when it comes to originally English visual novels