It is appstore that includes a repositorie of only free and open source (FOSS) apps. Does not need an account to work.
Amazon's own alternative to Google Play. Needs an Amazon account to work. Offers free and paid apps.There is also free paid app offer each day.
Yandex known as the Google of Russia launched its own appstore to compete in select markets. Does not need an account to download free apps. For paid apps, you may need an account.
While the number of all these stores combined pales in comparison to Google's own. They are quite good alternatives for those who want to different options and do not want to depend only on Google.