How to launch an IF game file
Many IF games can be played in a web browser, but if you download the game file, you'll need a launcher app (also called an "interpreter").
Below are download links for the most popular apps.
For Windows, Mac, and Linux, try the Lectrote app. This will launch most games and is clear and easy to read.
You can either choose the most recent release for your system from the Lectrote releases page, or download release 1.3.4 directly from these links:
For the Linux versions, unzip into a folder and launch the app from there. It won't show up in your main menu though.
For Android, try the Fabularium app:
For iOS, try the Frotz app:
If Lectrote won't work for you, try the Gargoyle app. It will also launch most text games, but doesn't seem to be updated as often as Lectrote.
Gargoyle for Windows
Gargoyle for Mac OS
For Linux users, the first place to look is the main repository for your distribution. If you're using Linux Mint, open the Synaptic package manager and search for Gargoyle.
Other options depend on the game format, which you can usually tell from the file extension.
(Extensions: .z3-.z8, .zblorb, .zlb, and sometimes .dat and .zip)
Mac OS: (?)
Linux: Frotz will almost certainly be in your distribution's main repository. It will play all the different versions of z-code files, including V6. If Frotz is not on your main repository then David Griffith's Frotz page lists several places to download it.
(Extensions: .ulx, .blb, .gblorb, .glb)
(Extensions: .gam, .t3)