List of file extensions

A

• .a3c - Alan 3 story file.
• .a3r - Alan 3 resource file.
• .acd - Alan 2 code file. Always accompanied with a .dat data file.
• .alr - ADRIFT Language Resource file.
• .asl - Quest source code and readable story file. Contrast with .cas.

B

• .blb - Blorb file, which contains other files, one of which is almost certainly some kind of story file. See also: .gblorb, .glb, .zblorb, and .zlb.

C

• .cas - Compressed Quest story file. Contrast with .asl.

D

• .dat - Data file. Without context, this could be anything. Infocom used .dat files for its story files; those are equivalent to any one of .z1 to .z8 file formats. Alan 2 also uses its own .dat files; these are always accompanied with an .acd file.

F

• .floydc - Floyd story file.

G

• .gam - TADS 2 story file.
• .gblorb - Blorb file which contains a Glulx story file.
• .glb - Blorb file which contains a Glulx story file.

H

• .h - Header file. This is a special type of source code file shareable between projects. Inform 6, TADS 2, and TADS 3 all use .h files.
• .hex - Hugo story file. (Probably short for "Hugo EXecutable".)

I

• .i6t - Inform 6 template files used by the Inform 7 compiler.
• .i7x - Inform 7 extension source code file.
• .inf - Inform 6 source code file.
• .inform - Inform 7 project folder.

J

• .jacl - JACL source code file.
• .j2 - JACL source that has been processed by a version 2 interpreter and is ready for execution.

N

• .ni - Inform 7 source code. The "ni" stands for "Natural Inform".
• .nx - Node-X story file.

S

• .sav - Saved game file. This extension is used by various interpreters, including TADS 2 and Z-code interpreters, although the file formats are not always compatible.
• .scr - Transcript of a Z-Code game. It's pure text, so changing it to .txt can't hurt and might help.

T

• .t - TADS source code file.
• .t3 - TADS 3 story file.
• .t3v - TADS 3 saved game file.
• .t3x - TADS 3 story file.
• .tab - TAB game datafile
• .taf - ADRIFT story file. (Probably short for "Text Adventure File".)
• .tag - T.A.G. story file. (A German IF format.)
• .tws - Twine story file. (Twine output files, however, end in .html)

U

• .ulx - Glulx story file.

Z

• .z1 - Z-Machine version 1 story file.
• .z2 - Z-Machine version 2 story file.
• .z3 - Z-Machine version 3 story file.
• .z4 - Z-Machine version 4 story file.
• .z5 - Z-Machine version 5 story file.
• .z6 - Z-Machine version 6 story file.
• .z7 - Z-Machine version 7 story file.
• .z8 - Z-Machine version 8 story file.
• .zblorb - Blorb file which contains a Z-Machine story file.
• .zil - ZIL source code.
• .zlb - Blorb file which contains a Z-Machine story file.

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TODO: I'm sure there's many more relevant file extensions than this, but, again, we gotta start somewhere.