Obviously, Duolingo is the best-known free app right now. I think it is a good option, if you can not afford babbel. But since it's free, there's obviously not as much development power behind it. And I'm saying that as a hardened debian user, so trust me, I already gave it the benefit of the doubt here.
But I simply think it does not offer great visuals, functionality or linguistic concept. You can basically get in your lessons and be rewarded by the app for just rushing through it. Some of the lessons are pretty weird and not contiguous.
On the other hand, babbel is expensive. Some people might find that motivating (I don't). However, it is pretty perfect for beginners. You will not find a more intuitively to use app out there. The UX is pristine and simple. Only the grammar section could be a little bigger (for the languages I tested).
Best app for learning German for beginners - Native Speaker Review
In my opinion, babbel really is probable the best app to learn German fast. Mostly, because it is pretty effortless, and it's platform-independent (can be used from any browser and also on your phone). Same goes for duolingo, but I find the UX quite depressing, to be frank. It looks like crap and yeah, that makes a difference. I personally like a pretty app over anything, because it motivates me if the UI is clean and relaxing instead of "web 2.0" style...
What do to after completing your course with an app? More language learning tips
I think, if you want to learn German fast, you really have to plan it out. An app might get you there half-way, as in the first 6-12 months (depending on your efforts) the app will totally be enough. But after that, you should look into other resources, such as simplified language books/magazines and videos, e.g. videos in slow German or with subtitles.
Who is that app for?
I'd say, Babbel is an especially beginner-oriented app (German language A1 level, European Framework (CEF)). Because at some point, you will just need additional material. It's not an all-in-one solution. But that's still super good and if you stick to the courses, you'll be able to speak conversational German within 6-12 months (depending on how much time you spend practicing).
About me
I make videos about German language, German grammar and German culture. So if you are looking for these kinds of things–hi! Welcome. Most of the upcoming videos are made for beginners like you. Advanced videos (slow German, conversational German) will follow soon.
German language & grammar tips
This is my German language passion project. I just always wanted to do something like this. My main channel (mostly about minimalism and hiking) and my socials can be found below ↓↓↓ I don't really have a page for this project like a learning platform or anything, but if you have questions, you can contact me on Instagram, on TikTok (also German language & culture content) or in the comment section of course.
YOUTUBE · https://youtube.com/UndineAlmani/
BLOG · https://undinealmani.com
INSTAGRAM · https://instagram.com/undine.almani
My Babbel link* https://share.babbel.com/x/4XMmHQ
*I don't earn anything from this, but you get 3 months of a free trial if you use the link. I'd get some voucher for 10 bucks, I think, but other than that, this is not an affiliate link or anything and I'm not associated with Babbel in any way. The video reflects my opinion and your experience may differ, as language learning is a super individual thing.