Yes, the Windows Store offers a Mobile App that is best for lighter Windows OS such as the Surface and Windows Mobile. You should also be compatible with the Web App when using Chrome (best performance).
I'm talking about the one you get from clicking the Get Add-ins button in o365 Outlook Desktop version. This brings up a "store" where you can get a GTM plugin. Is it the same one as you get from the GTM website?
@MEmbry That might be a version of the brand-new plugin for O365. If it states 'GoToMeeting', then that's the only one. There are no imposters =)
You can safely install that at no risk. The functionality is almost the same, but with more reliability.