The most popular is Ren'Py; it's open source, free, and easy to use if you want to create a visual novel.
The downside is that if you want something more complex than the basics, you have to write Python code.
The upside is that, being so popular, it's full of tutorials and people willing to help you with any questions.
If you're looking for something that's more text-based and less graphical (though you can still include graphical components), I recommend focusing on "interactive fiction" instead of "visual novels," and there you can try Twine, which allows you to create content similar to "choose your own adventure" books.