They both are built on top of the Steem Blockchain.

Steemit is a content platform that hosts written long form posts. People write blogs, article, anything that is written. Imagine Medium.com on the best blockchain on the Content Web.

Musing is a content platform that caters to Question and Answers. People asks questions and get answers. Imagine Quora on the same best blockchain on the Content Web.

It's more meaningful to point out the similarities between the 2 platforms;

1) They were built on top of the Steem Blockchain. So many other Blockchain with hundreds of millions in investments tried to come up with "killer applications" but the Steem Blockchain have silently operating dozens of them with no issues.

2) Access 30+ (and counting) apps with only 1 account. If you think your Google Account lets you use many different types of apps for free, try count how many apps there is that requires only your Steem posting key. Steemit and musing are but only 2 out of many.

3) No Ads..

4) Get rewarded for your contribution, when people like what you produce, you get rewarded.. No need to get millions of views to start monetizing.

Hope you understand the serious Game Changer you have come across powered by the Steem Blockchain Technology.