Overview

Geolith is a free emulator for Neo Geo AES and MVS consoles and Neo Geo CD and CDZ systems, aimed at players who want one emulator across cartridge and disc formats. Its careful synchronization and broad system support make it a strong option for preservation-minded users, provided they can supply the required BIOS files and accept a few hardware and timing limits.

Part of Jolly Good Emulation, a project focused on reusable, simple, readable software, Geolith is built around The Jolly Good API. It can also run as a standalone binary or in multi-emulator frameworks; compiling it requires that API’s header files. The README identifies the license as BSD-3-Clause.

Key features

Geolith emulates CPUs at instruction-level granularity and synchronizes them with each other, the LSPC video system and YM2610 sound. That gives the project a strong foundation for accurate play, but its video-event timing is best effort, not cycle-accurate. Games are described as playable with minor differences from real hardware and no known major bugs; cycle-accurate rendering remains a longer-term goal.

Cartridge systems accept TerraOnion .NEO files only. CD systems use .bin/.cue images and optionally .chd, so users with other cartridge formats will need a conversion or a different emulator. BIOS files from a recent MAME set are required, and the required archives vary by system.

Settings cover AES, MVS or Universe BIOS mode, CD system, region, free play, memory-card options, palette and aspect ratio. Input support extends from Neo Geo joysticks to the Mahjong Controller, four-player extension board, V-Liner and Irritating Maze trackball, a useful range for specialized games and controller setups.

The latest changelog entry, version 0.4.2, fixes an LSPC state leak when switching between CD and cartridge games and adds support for The Jolly Good API 2.0.0.

Pricing

Geolith is free, with no free trial or paid plan to weigh against its core features. The cost is practical rather than financial: players must provide compatible game images and the required BIOS files.

Platforms

Geolith supports Linux, macOS, Windows and BSD. Build instructions cover those platforms, with Windows builds using MSYS2; compiling also requires The Jolly Good API header files. That makes the platform range broad, though the API dependency may be a hurdle for users who want to build from source without framework components.

Who it's for

Geolith suits Neo Geo players who want AES, MVS and CD-family emulation in one free project, especially those using supported controller hardware or interested in configurable BIOS, region and memory-card settings. It is less suitable for users who need dedicated JAMMA PCB support, PAL mode, an early Stakes Winner prototype, or cartridge formats beyond .NEO.

Pros and cons

Pros: Supports AES, MVS, CD and CDZ, with compatibility stated for commercially released AES, MVS and CD games.
Pros: Instruction-level CPU emulation and synchronization with video and sound components prioritize faithful system behavior.
Pros: Broad controller support and settings for BIOS mode, region, free play, memory cards, palette and aspect ratio accommodate varied setups.
Cons: Cartridge support is limited to TerraOnion .NEO files, and a recent MAME BIOS set is required.
Cons: Video timing is best effort rather than cycle-accurate, and dedicated JAMMA systems and PAL mode are unsupported.
Cons: The early Stakes Winner prototype cannot currently be emulated because required data is missing.

Alternatives

Choose Neo Geo Emulators to compare more options by category. NeoRAGEx is a free Windows-only emulator; games and BIOS are not included. NeoDS is free to use for non-commercial purposes. GnGeo is a free Linux option that requires SDL 1.2.x, libz and a Neo Geo BIOS; commercial use of GnGeo as a whole is forbidden by its license notes. GxGeo is another free alternative.

NeoCD/SDL is a free Linux and Windows option for CD emulation; it requires an original Neo Geo CD BIOS, and its selling, source-code reuse and technical knowledge are restricted to non-commercial purposes. MVSPSP is another free alternative. Mac users considering a paid option can choose NeoBox, a $14.99 one-time Mac app that requires macOS 14 or later and your own ROMs and BIOS files. NCDZPSP is another free alternative.

Verdict

Geolith is a strong free choice for players seeking broad Neo Geo AES, MVS and CD-family support, configurable systems and an unusually varied range of controllers. Choose it if .NEO or supported CD images and MAME BIOS files fit your setup; look elsewhere if you need PAL or JAMMA support, cycle-accurate video timing or a different cartridge format.

	Geolith	Nesalizer
Free plan	No	No
Free trial	No	No
Paid from	—	—
Open source	No	No
Platforms	Linux, macOS, Windows	Linux, Windows
Free plan	Yes	—
Supported platforms	Windows, macOS	Linux/POSIX; Windows (experimental port)
Save states	—	Yes
Rewind	—	Yes

Geolith vs Nesalizer

Geolith

Nesalizer