openacid/slim is a Go library for building memory-efficient, serializable trie indexes and sparse arrays, primarily designed for in-memory indexing of large on-disk key-value data. The core artifact is SlimTrie, a compressed trie that achieves roughly 11 bits per key while supporting fast Get, range queries, prefix scans, and versioned marshal/unmarshal. The repository also contains a standalone sparse-array package and a type-safe encoder framework, with extensive benchmarks comparing against Go maps and btree indexes. Its architecture is modular: the trie package defines the index structure, the array package provides bitmap-backed dense/sparse storage primitives, and the encode package abstracts value serialization with generated concrete implementations.