A generic, reusable implementation of topological sorting with cycle detection (Tarjan's algorithm). It is self-contained, depends only on standard Kotlin collections, and can be extracted for any project needing dependency ordering or cycle validation. Demonstrates clean separation of concerns and efficient graph traversal.

An optimized protobuf writer that encodes fields in reverse order to compute length-prefix sizes without buffering. This is a non-obvious performance pattern for nested messages, reducing memory allocation. The class is small, self-contained, and could be reused in any protobuf implementation requiring efficient encoding.

A hand-written recursive-descent parser for `.proto` files that produces an AST (`ProtoFileElement`). It handles comments, options, imports, packages, messages, enums, services, extensions, and groups. The parser is self-contained, well-tested, and could be extracted for any tool needing to parse protobuf schemas without relying on `protoc`.

A custom immutable list implementation optimized for protobuf repeated fields. It provides O(1) size, iterator, and get operations, and supports efficient `MutableOnWriteList` for copy-on-write semantics. This is a reusable pattern for any Kotlin project needing a lightweight, read-optimized list without the overhead of Kotlin's standard immutable collections.

A multiplatform gRPC client interface with expect/actual implementations for JVM and non-JVM platforms. It provides a clean abstraction for unary, server-streaming, client-streaming, and bidirectional streaming calls. The design is decoupled from transport (OkHttp on JVM) and could be reused as a base for custom gRPC clients.