Embedded systems:

• Embassy for async Rust
• Heapless for statically-allocated data structures or allocate as much as possible on the stack
• Patina implements the UEFI interface

Operating systems:

• Rust for Linux
• Android with firmware, virtualization framework and other os features

Runtime and virtualization

• Firecracker
• Deno as JS runtime and it proved that in just a fraction of the time and developers, Deno already has shipped way more features than Node.js.

Cross platform apps

• Signal uses Rust
• Proton uses Rust to build cross-platform applications

Dropbox, Element (matric Chat), Ditte and others also uses Rust.

Databases

• Neon uses a single S3-compatible storage as its backend. It complicates Postgres' monolithic architecture but it also solves many of its problems: read-replicas now uses a single source of truth instead of (error-prone) replication; slow and expensive networked storage are not needed anymore to get a highly-available database and upscaling or downscaling is a matter of spawning a new container/microVM
• Datafusion is an extensible query engine that allows data engineers to query data sources from Rust or Python with a high level interface, or build data systems using it as their query layer to build and optimize query plans. See the projects build with it!
• [Turso] is an embedded, SQLite-compatible database written in rust. It's fully open source compared to the private test suits of SQLite. It solves many SQLite pain points: easy database encryption, concurrent writes, async I/O, updating the schema and more.

Servers: the author project Pingoo

As mentioned earlier, one of the many interesting things that Rust enables, is to reuse patterns from the embedded world, such as eliminating heap allocations to be as performant as possible

Nearly all Blockchain projects are using rust.