Nami is a browser based wallet extension to interact with the Cardano blockchain and is non-custodial.
It can be used to send and store multiple assets, to delegate, to mint tokens, use multi-sigs and much more. Smart contract support will be added when available.
The main difference to current wallets is, that Nami can be injected into the browser context and be connected to any website in order to interact with dApps (decentralized apps).

Yes and no. Nami will not track all addresses associated with your imported wallet, and might result in partial reflection of assets. Daedalus/Yoroi utilize the concept of multiple addresses per wallet, while Nami just uses a single address.
Nami also allows to create sub accounts from a single seed phrase. All accounts except the first one are hidden from Daedalus/Yoroi. We don't recommend using Nami and Daedalus/Yoroi simultaneously, but rather use the seed phrase to migrate from one wallet to another.
If you want to migrate from Daedalus/Yoroi send all your funds to the address you see in Nami after importing the seed phrase.
We still prefer to create a new wallet for Nami to avoid confusion and keep the user experience great.

Nami is completely free to use and open-source. To fund the project and keep the development up we appreciate delegations to Berry and we also consider using Project Catalyst for additional funds.

You can only import one seed phrase, but from that one you can create sub accounts. Each account is its own wallet and independent from each other. There is no reference to the other account on the blockchain, which gives Nami some kind of privacy and anonymity, when distributing funds accross multiple accounts.
With each account you can delegate to different pools.

Yes, you can delegate your ADA to pools. External staking interfaces can be built on websites, where Nami can be connected to. Inside the wallet itself there is the option to delegate to Berry. If you enjoy using Nami, consider delegating to Berry. It helps us a lot to keep up the development.

Transactions on Cardano are normally validated in phase 1, which means before they even get onto the network they are completely verified. If something is off, such as inadequate fees or an insufficient balance, the transaction is directly rejected without incurring costs.

Smart contracts (Plutus validators), on the other hand, are validated in phase 2. Only the node that produces the block verifies the contract fully. In the event of a contract failure, a collateral is taken to cover the resources (cpu and memory) used by the node to verify the contract. When a script runs successfully, the collateral is not taken.

The chances of losing the collateral are very low; however, Nami seeks to minimize the risk by only allowing a determined amount (5₳) of collateral to be used. In a worst case scenario, malicious, or poorly built dApps, would only be able to take this amount.
Finally, collateral aims to prevent bad actor from spamming the network with failing contracts.