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 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 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.