File extension rmskin is used by following file type(s):

File extension rmskin file type description:
Rainmeter skin file

The RMSKIN file extension is associated with the Rainmeter, one of the best known and most popular desktop customization programs for Windows.

A .rmskin file is a ZIP compressed skin package, that includes various add-ons, fonts, plugins, skins, theme and more. 

that open rmskin files:
Rainmeter (Microsoft Windows)