| Name | Status | Java versions (from … last known) | Short description | Platforms supported | Garbage Collection (GC) | Execution Mode | JIT Compilers | TCK / License Status |
|---|
| Active / Maintained |
|---|
ParparVM
(Codename One) | Active | 8 … 8 | Translates Java bytecode to C code; used by Codename One. | iOS, Android, Desktop targets, UWP / native app targets via native toolchain. | Boehm GC (conservative), Simple Mark & Sweep available. | AOT (Transpilation) | C Transpiler | No TCK.
(Project sources / Codename One). |
| Substrate (used by GraalVM JDK) | Active | 1.8.0_212 … 25 | Polyglot VM based on HotSpot/OpenJDK; native-image & multi-language Truffle support. | Linux (x86_64, aarch64), macOS, Windows. | G1, Serial, Epsilon (HotSpot GCs). | Mixed / AOT | C1/C2 JIT, Graal JIT (Native Image) | TCK/certification varies by distributor. |
| HotSpot | Active | 1 … 25 | The widely used OpenJDK VM implementation (Oracle / OpenJDK HotSpot). | Cross-platform: Windows, Linux, macOS; primary ISAs: x86-64 and AArch64. | Serial, Parallel, G1, Epsilon (E), Shenandoah, GenZGC, GenShen more... | Mixed (Interp + JIT) | C1/C2 Compilers (Graal optional) | Yes (Reference VM in OpenJDK). |
| OpenJ9 | Active | 8 … 25 [1] | IBM J9-based open-source VM (Eclipse OpenJ9). Optimized for cloud/memory. | Linux (x86_64, ppc64le, s390x, aarch64), Windows, AIX. | Gencon / Generational Concurrent (default), Balanced, Metronome, OptThruput. | Mixed (Interp + JIT + AOT) | OpenJ9 JIT (Optimizing Compiler) | Source-open; binary TCK depends on distributor (e.g., IBM Semeru). |
| IKVM | Active
(Community forks) | 1.4 … 8 | Java on .NET / Mono; bytecode-to-.NET and interop. | Runs on the .NET runtime(s). | CLR GC (Relies on the underlying .NET GC). | JIT / AOT | CLR JIT (Code generation by host runtime) | No TCK. |
| Jikes RVM | Active
(Research) | 6 … 6 | Jikes Research VM — meta-circular research VM. | IA-32 Linux and PowerPC 64 Linux (historically). | MMTk (Memory Management Toolkit); modular collectors. | JIT Only | Baseline, Optimizing Compilers | No TCK.
(EPL). |
| leJOS | Active
(Robotics) | 1.5 … 1.6 | Robotics firmware / Java environment for Lego Mindstorms RCX/NXT/EV3. | Runs on LEGO Mindstorms hardware families; embedded firmware. | Compact GC (Mark and Sweep). | Interpreter | N/A | No TCK. |
| Maxine | Active
(Research) | 7 u6 … 8 u222 [2] | Meta-circular research VM from Oracle Labs / Univ. of Manchester. | x86_64 (Linux/macOS), AArch64 (Linux), experimental RISC-V. | Maxine Heap (Java-written heap & collectors). | Mixed (Interp + JIT) | Research JIT Tiers | No TCK (research project). |
| Inactive / Archived / Maintenance |
|---|
| Cacao | Inactive / Maintenance | 1.5 … 6 | JIT-based VM; used historically with GNU Classpath/OpenJDK. | Multi-arch historical ports: Linux, macOS, ARM and x86. | Boehm GC (typical/historical). | JIT | Platform JIT | No TCK. |
| Apache Harmony | Inactive
(Retired 2011) | 5 … 6 | Clean-room OpenJDK alternative (DRLVM); discontinued. | Targeted cross-platform JVM work (Linux, Windows, macOS ports historically). | Generational GC (Mark-Compact / Copying). | Mixed (Interp + JIT) | DRLVM JIT | No TCK. |
| Kaffe | Inactive | 1.2 … 1.4 | Clean-room JVM implementation (historic). | Portable C-based VM; builds available for many POSIX platforms. | Conservative / Mark-Sweep (Kaffe GC variants). | Mixed (Interp/JIT) | Platform JIT | No TCK. |
| GNU Compiler for Java (GCJ) | Inactive | 1.4 … 1.5 | Ahead-of-time Java compiler in GCC (removed). | Historically targeted many Unix/CPU combos. | Boehm GC (historical ports). | AOT | GCC Backend (Native Code Generator) | No TCK. |
| JamVM | Inactive / Rare updates | 5 … 8 | Small, embeddable JVM often used with GNU Classpath or OpenJDK. | Cross-platform (Linux, BSD, macOS). | Mark and Sweep (compact). | Interpreter / JIT | Optional JIT | No TCK. |
| JOP | Inactive/Academic | 1.1 … 1.1 | Hardware JVM for embedded real-time systems. | Dedicated hardware (JOP processor family / FPGA/ASIC targets). | Hardware-assisted GC (real-time). | Hardware (Execution) | N/A | No TCK. |
| Juice | Inactive | 1.1 … 1.1 | Experimental Java ME JVM (NUXI OS). | Platform: niche embedded target (NUXI/experimental hardware). | Unknown. | Interpreter | N/A | No TCK. |
| Jupiter | Inactive | 1.4 … 1.4 | Research JVM using Boehm GC and GNU Classpath. | Historically Linux/x86 ports documented. | Boehm GC. | Interpreter | N/A | No TCK. |
| Mika VM | Inactive | 1.3 … 1.4 | Embedded JVM (successor to Wonka). | Embedded/IoT targets (platform-specific firmware). | Compact GC. | Interpreter | N/A | No TCK. |
| NanoVM | Inactive | 1 … 1 | Tiny JVM for Atmel AVR (Asuro robot). | Atmel AVR microcontroller (Asuro) hardware. | Simple GC. | Interpreter | N/A | No TCK. |
| SableVM | Inactive | 1.3 … 1.5 | Research-oriented portable interpreter. | Cross-platform Unix-like systems and research hosts. | Copying GC. | Interpreter | N/A | No TCK. |
| Squawk virtual machine | Inactive | 1.1 … 1.1 | Sun's small Java ME VM for embedded devices (Sun SPOT). | Sun SPOT / small embedded device platforms. | Pausing GC (embedded-friendly). | Interpreter | N/A | No TCK. |
| SuperWaba | Inactive | 1.2 … 1.2 | Java-like VM for portable devices; succeeded by TotalCross. | Embedded/mobile device targets historically. | Mark-Sweep. | Interpreter | N/A | No TCK. |
| TakaTuka | Inactive/Archived | 1.1 … 1.1 | JVM for wireless sensor motes (Tuk compact format). | Sensor-mote platforms (TinyOS-like / constrained hardware). | Unknown. | Interpreter | N/A | No TCK. |
| TinyVM | Inactive | 1 … 1 | Small RCX replacement firmware VM. | RCX-like embedded brick hardware targets. | Compact GC. | Interpreter | N/A | No TCK. |
| VMKit | Inactive / Archived | 1.4 … 1.5 | LLVM-based VM substrate (archived). | Cross-platform via LLVM backends (Linux/x86_64 etc.). | MMTk. | JIT | LLVM Backend | No TCK. |
| Wonka VM | Inactive | 1.3 … 1.4 | Embedded Wonka VM (Acunia). | Embedded hardware / specialized boards (historic). | Generational GC. | Interpreter | N/A | No TCK. |
| Java Operating Systems |
|---|
| JX | OS-level (Research) | N/A | Java operating system (University of Erlangen). | OS-level VM (research platforms). | Precise GC. | Mixed (AOT/JIT) | AOT/JIT | No TCK. |
| JavaOS | OS-level (Legacy) | N/A | Original Java-based OS from Sun Microsystems for network computers (NCs) and embedded devices. | Dedicated network computers (NCs), embedded systems. | Classic GC (Mark and Sweep/Compact). | Mixed (Interpreter/JIT) | Standard Sun JIT | No TCK. |
