Icu4x

Bttf is a Rust-based CLI tool for datetime arithmetic with extensive usage examples and an active repo (latest release 0.1.4, 490 stars, 10 forks).

Biff is a Rust-based CLI for datetime arithmetic/formatting with active repo activity, installation options, licensing, and extensive usage examples; latest release 0.1.3 (May 27–28, 2026) with 351 stars.