If you're a fan of classic RTS games, this is a pretty good week! Not only has the Command & Conquer Remastered Collection just arrived, but the Total Annihilation: Commander Pack is currently free to grab as well.
Simply head on over to GOG, secure yourself a copy, and you'll soon be ready to unleash a ridiculous amount of units upon your foes. The only downside is that the promotion will last for about one day, until 1pm UTC on June 7th, so do make sure to grab it as soon as you can, lest you forget.
In terms of content, the Commander Pack contains the original Total Annihilation, as well as both of its expansions: The Core Contingency and Battle Tactics. What it doesn't contain is fixes for some of the more annoying issues, so you might also want to grab the community patch before you start playing. It's not exactly mandatory, but if you go and browse through the patch notes, you'll quickly realize just how useful it is to have.
Whatever you choice may be, I hope you have fun - Total Annihilation is a classic RTS for good reason!