Different file types used in Mx Simulator.
PNG's are the most common file type for images, works for most things.
PPM files has the same function as PNG files, but works in a few more cases even if it is far less used.
The .pgm file is only used for the shadows.pgm file.
JM files are propietary for Mx Simulator. They tell the game how the PNG template should be applied on the JM files shape. It's essentially the object shape without collision and texture.
Shape files (.shp) holds collision info for an object.
SAF (Simple Archive Format) is an archive used in the game. Instead of having a folder or a bunch of files, you can pack them into a single file for ease of use.
GNU Zip (.gz) is a compression format typically found in Unix systems. Altough Mx Simulator can read this format, it's very rarely ever used.
A lot of files in Mx Simulator are extensionless, meaning they don't have an extension such as .png, .saf, .mp3 etc. They're used for a variety of things.
Sequence files (.seq) replays things in sequences, such as making objects appear/disappear or replay a texture making it seem like it rains.
Trackinfo files contains information about which track it is for and a hash that's based on necessary files for the track, ensuring that everyone uses the same version. This filetype is used for running servers.
Archives not used in game
To save space when uploading/downloading files, a variety of archives are used to compress the files and folders. Most common is .rar, .zip and .7z. These files cannot be read by the game (like .saf can), so they need to be extracted before put into the game. WinRAR is the most popular choice, but there is also other programs such as 7-zip or WinZip.