Action1 is an endpoint manager that allows you to update computers, run automations, and even remotely install software. They have a free version right now that will allow up to 200 endpoints, and the unique thing about this site is that they don't limit the free version to a few features. All the features are free, and it even comes with built-in remote access. It only currently supports Windows and MacOS, but Linux support seems to be on the horizon if you look at the roadmap. It should be available after the two next releases.
https://www.action1.com/free-edition/