Tagboard adds support for using tags with scoreboard objectives. For example, this is how you'd create an objective for mining any types of flowers:
/scoreboard objectives add flower minecraft.mined:#minecraft.flowers "Flowers mined"
Tagboard is mostly server-side: You can add tag objectives without Tagboard installed on the client, but the completion displays an error. (This is a vanilla limitation that I can't fix without modding the client.) With Tagboard on the client, the completion works properly as well.