Amplitude.com is free and pretty powerful tool.

I'm trying to move away from Paddle. While it's good for start, it has a lot of limitations that can really slow down the business once it starts to scale.

If Stripe is not available in your country you can try Braintree or Paymill in EU. Paymill however requires a lot of paperwork and activating your account can take weeks (I've been there).

Bold move. I'm curious of the reactions here. One of my products is also based on Streak and I noticed many people leaving after breaking it. It's a bit different target group though and I don't think anyone would pay $50 for fixing 50-day streak in my community.

Pieter suggested adding Personal Record - that might be a good idea. You could still brag about longest streak and have a goal of beating your own high score.

At tookapic.com I use Paddle and they simplify taxes a lot for me. However along with that comes a lot of limitations. Their support reply time is also very slow. The API does not offer everything I'd want. For few weeks I used fastspring.com which does pretty much the same, but still - even more limitations in terms of design.

So for simple payment solutions there's Paddle.com and Fastspring.com. If you want something more advanced and flexible, I'm afraid you'd need to pay extra for services like Avalara.