Babbel kind of takes traditional textbook style learning, and adapts it quite well to technology. It's also built around really colloquial conversations, and the audio is high quality. I would say it tends to focus more on how people actually speak than textbook-style speech

Rosetta Stone was the big player before Duolingo. They had a method that involved not using your mother tongue, which they called 'immersion'. I believe in the recent years (since Duolingo ate their pie) they have moved more and more towards dueling style learning. They have an app that's a lot more corporate, but I've heard good things about it too

Note, I haven't used either of these applications in years, I just work in the space and this is my understanding of them

They are also language learning apps. Different style than Duolingo, but still worth the price imo