If it is too slow paced for you, then you are not looking for duolingo alternative. You are looking for something entirely different. The whole Duolingo deal is fun, relaxing, low effort learning in exchange for slower progress.

And of course there are competitors, many of them. There are also many free language learning resources. But, you did not said which language you are learning and whether you are beginner or not. And most of free resources are made for specific language.