Machine tags (MachineTag) are just standard tag with extra information to extend the information in the tag. They are called machine tags because there are often use by program to get extra information from the tagged work.
This machine tag (fs_rating) is used to rate Free Software project. The rating is between 0 and 5 (of course, you can use any other value) and here is a subjective evaluation of the fs_rating metric.
|rating value -||perception of the rating (a bit subjective ;-)|
|0||This is not free software, you don't want to use it, I hate this free software.|
|1||This is free software but a lot of work need to be done to make it usable.|
|2||This is free software, there is space for improvement but already capable to be useful.|
|3||This a good free software but some minor issues.|
|4||This is very good free software with no real issues.|
|5||This is excellent free software.|