The file appears to be a specific development or community-distributed build of s&box (pronounced "sandbox"), the spiritual successor to Garry's Mod developed by Facepunch Studios . Project Overview
While official public builds are typically managed through Steam's Library tab , numbered builds like often originate from: S&Box.Build.10376186.zip
The preview period recently closed in preparation for the public launch. The file appears to be a specific development
Large build IDs often correspond to specific depot updates on SteamDB. S&Box.Build.10376186.zip
The platform is free to use with no royalties or strings attached for creators. Build Analysis: 10376186
Zip files with these naming conventions are frequently shared in developer communities or via "giveaway" systems before the official Steam release.