FreeBSD's Geli (GEOM-based Disk Encryption Layer) provides disk encryption features for data at rest on FreeBSD systems. Here are some of its key features:

1. Full Disk Encryption: Geli allows you to encrypt entire disks or individual partitions, ensuring that all data on the disk is encrypted.

2. Encryption Algorithms: Geli supports various encryption algorithms, including AES (Advanced Encryption Standard) in different key sizes (128, 192, and 256 bits). You can choose the algorithm and key size according to your security requirements.

3. Authentication Methods: Geli supports several authentication methods, including passphrase-based authentication and key files. Passphrases can be used to unlock encrypted disks during system boot or while the system is running.

4. Multiple Keys: You can configure multiple keys for a Geli-encrypted disk, allowing multiple users or systems to access the encrypted data.

5. Key Management: Geli provides tools for key management, including key generation, addition, deletion, and rotation. These tools allow you to manage encryption keys effectively.

6. Checksumming and Integrity: Geli uses cryptographic checksums to ensure data integrity. If data corruption occurs, Geli can detect it, providing an additional layer of security.

7. Pluggable Architecture: Geli is designed with a pluggable architecture, allowing easy integration with different encryption algorithms and modes. This flexibility enables users to choose the most suitable encryption options for their specific use cases.

8. Performance Optimization: Geli is optimized for performance, ensuring that encryption and decryption operations have minimal impact on system performance. This optimization allows FreeBSD systems to maintain good performance even when using disk encryption.

9. Integration with GEOM Framework: Geli is integrated into FreeBSD's GEOM framework, which allows for easy configuration and management of encrypted disks through the geom utility. GEOM provides a modular framework for storage management in FreeBSD, and Geli leverages this framework to provide disk encryption capabilities.

It's important to note that specific features and capabilities might vary depending on the version of FreeBSD you are using. Therefore, it's recommended to refer to the official FreeBSD documentation or man pages for the most up-to-date and detailed information on Geli encryption features for your particular FreeBSD version.