Tailcall is a Rust library that provides stack-safe tail calls on stable Rust. It uses a lightweight trampoline runtime (Thunk) along with a proc-macro attribute `#[tailcall]` that transforms recursive functions. The macro can lower simple self-recursive functions into a direct loop (zero overhead), while more complex cases (mutual recursion, borrowed state) fall back to a type-erased fixed-size closure runtime. The core runtime is `no_std` compatible and uses inline storage for closures without heap allocation. The workspace includes the main `tailcall` crate (runtime), `tailcall-proc-macro` (proc-macro implementation), and integration test crates for both `std` and `no_std` environments, plus benchmarks demonstrating performance competitive with handwritten loops.