Blizzard just released the 1.18 patch for StarCraft: Brood War, improving compatibility with modern systems and making both StarCraft and the Brood War expansion completely free, forever, no catch.
Here's where you can download it:
https://starcraft.com/en-us/articles/20674424
Bonus: When StarCraft: Remastered comes out, players on classic StarCraft will be able to play with Remastered players.
I imagine most people who are interested in RTS games have played this classic some time in the almost 20 years since its release, but just in case here you go