The current version of Twine is “Twine 2” and Harlowe. I believe there are users who still swear by Twine 1 (1.4?) and/or Sugarcube. I agree with checking those out, along with some other systems that are even potentially easier than Twine - like Squiffy and Ink and AXMA 6.1 (I still can’t get my head around the JS AXMA version, but 6.1’s “early twine” syntax is a lot more straightforward for me than Harlowe’s markup and “gift tags”.)
Check out our list of resource links that includes more IF systems. And please add any others you know about - this post is a Wiki that can be edited by our regular users.