Files with w3m file extension can be generally found as map files for Warcraft 3 computer games.
Software that open w3m file
W3M file extension - Warcraft 3 map
What is w3m file? How to open w3m files?
The w3m file extension is used for maps in Warcraft III computer game.
The w3m file is a Warcraft III Map file (AKA Warcraft III Scenario in the World Editor).
It's just a MPQ (using a "new" compression format) with a 512bytes header. Sometimes, for official W3M files, it uses a footer of 260 bytes for authentication purposes.
The default software associated to open w3m file:
Company or developer:
Blizzard Entertainment, Inc.
Warcraft III: Reign of Chaos is a real time strategy video game released by Blizzard Entertainment in 2002. It is a third game from popular Warcraft franchise.
Warcraft III: The Frozen Throne 
Company or developer:
Blizzard Entertainment, Inc.
Warcraft III: The Frozen Throne is a real-time strategy computer game developed for Microsoft Windows, Mac OS and Mac OS X by Blizzard Entertainment and released in 2003. It is the official expansion pack to Warcraft III: Reign of Chaos.
List of recommended software applications associated to the .w3m file extension
Recommended software programs are sorted by OS platform (Windows, macOS, Linux, iOS, Android etc.)
and possible program actions that can be done with the file: like open w3m file, edit w3m file, convert w3m file, view w3m file, play w3m file etc. (if exist software for corresponding action in File-Extensions.org's database).
Software that open w3m file - Warcraft 3 map
Programs supporting the exension w3m on the main platforms Windows, Mac, Linux or mobile. Click on the link to get more information about listed programs for open w3m file action.
Microsoft Windows:
Main software associated with w3m file by default:
Warcraft III: Reign of Chaos
Warcraft III: The Frozen Throne
