Blizzard has made available some classic games for free for WIndows and Mac OS.
Refer to the article below from PC Mag for details.
"Some require you to connect with Battle.net and set up an account with Blizzard, while others may simply download to your computer and play locally. Here are the classic Blizzard games you can now play for free:
World of Warcraft®
Warcraft® III: Reforged
Heroes of the Storm®