Built by a dutch non-profit, Medito is a meditation app that is completely free without ads, supported by donations from the community. The new update brought a completely new interface and new content.
The source code is on GitHub and the app is available for iOS and Android. Sadly the F-Droid version didn’t receive the update yet.
I’m not affiliated with Medito, just a meditator who has used Medito for 3 years now. It helped me a lot, and maybe it can help some of you too. Have a nice day.
For guided mindfulness meditation, I’m not sure you need an app, just a recording. I have used these free recordings for years: Mindfulness: Finding Peace in a Frantic World
Another good resource that I made a lot of progress with when I was first starting out is UCLA Mindfulness Awareness Research Center recordings of their weekly mediation sessions. https://www.uclahealth.org/programs/marc/free-guided-meditations/drop-meditations-hammer-podcast