To begin, it's important to make a clear distinction between different areas of "mrgn", a growing ecosystem of entities and projects that may confuse new users.
MRGN, Inc: The company which initially developed the marginfi protocol, along with some associated web interfaces, software development kits (SDKs), data analytics, and risk management systems.
The marginfi Protocol:Intentionally branded in all lowercase, marginfi is a suite of persistent smart contracts that together create a composable defi-native prime brokerage, a protocol that facilitates peer-to-peer lending and portfolio management of trader positions across blockchains.
mrgnlend: mrgnlend is an overcollateralized borrow/lend protocol embedded within marginfi. It's the only product live in the marginfi ecosystem today. mrgnlend allows you to borrow, and it allows you to lend.
The marginfi Interface: A web interface that allows for easy interaction with the marginfi protocol. The interface is only one of many ways one may interact with the marginfi protocol.