All of the systems I've talked about so far are well established. However, there are newer systems available that are built on the foundation of older systems, namely TADS 3 (often called T3) and Glulx.

TADS 3

TADS 3 is the latest version of TADS,. TADS 3 uses a different virtual machine than TADS does. T3 game files end in .t3x, to distinguish them from older .gam files. T3 interpreters are available from TADS.org.

Glulx

Glulx games are written for a virtual machine developed by Andrew Plotkin. They are often larger and can have more features than older Z-code games. Glulx game files end in .ulx, .gblorb, .blb, and .glb.

If your system runs Windows, Mac OS, or Linux, try the Lectrote interprer. For a mobile device, try Frotz for iOS or Fabularium for Android.

You can find Glulx games at IFDB or the Interactive Fiction Archive.