The problem dOST.cash solves

Digital cash in every day life. Spending ETH, DAI or OST for everyday actions -directly- would expose your private life on the blockchain. We can use ephemeral (burner) keys that we reuse minimally, but chain analysis would still reveal where the funds came from.
We use ring-signatures in the dOST.cash wallet to mix and obfuscate the funding of burner keys, which you can then you use as anonymous digital cash. (We proudly build on Heiswap.)

We make the experience intuitive by introducing a "spending" wallet page (with burner keys), and a "savings" page, where the secured (larger, and anonymous) funds reside. We exploit this, as moving over the ring-mixer takes some time, as does moving funds from Layer-1 (more secure), into Layer-2 (fast and cheap).

People can instantly receive their first crypto, as simple as opening dost.cash on their phone, generating their first wallet in the browser. They can then later setup a secure smart contract wallet (using OpenST) which is recoverable with 6digit-PIN and a single friend.

dOST.cash can manage funds natively on Layer-2 (and Layer1), allowing for fast and cheap (micro)transactions. By building on Mosaic as a layer-2 scaling solution, we can run EVM contracts at internet scale:
solve UX with smart contract-based fund recovery, and
establish privacy with ring signatures (and later zkSTARKs)

Challenges we ran into

The project scope was massive. Designing the UI; writing the React-app from scratch; integrating Elliptic Curve Cryptography, even when we directly build on the awesome work done by Kendrick (Heiswap). We're exhausted and haven't slept ?