It's been around for a while, and it's great. It only recently changed its name to Organic Maps.
This is the history of it, originally called Maps.me:
Maps.me was founded by Yury Melnichek, Alexander Borsuk, Viktor Govako and Siarhei Rachytski. Under the leadership of Alexander, MapsWithMe onboarded 2.5M users worldwide.
In November 2014, it was acquired by Mail.Ru Group and became part of its My.com brand. In September 2015, the app was open sourced and a free and open-source software version was additionally made available on F-droid.
In November 2020 Mail.ru Group sold Maps.me to the payment processor Daegu Limited, part of Parity.com Group. Daegu Limited changed the application user interface and content. Following this acquisition, in January 2021, a fork — Organic Maps —was created by a developer community.
It is now probably the best open source map app. Here's their github, and fdroid