diff --git a/SModule b/SModule
index 3e96f9f..845eb17 100644
--- a/SModule
+++ b/SModule
@@ -17,6 +17,7 @@ mijin_sources = Split("""
     source/mijin/util/os.cpp
     source/mijin/types/name.cpp
     source/mijin/virtual_filesystem/filesystem.cpp
+    source/mijin/virtual_filesystem/memory.cpp
     source/mijin/virtual_filesystem/stacked.cpp
 """)
 
diff --git a/source/mijin/virtual_filesystem/memory.cpp b/source/mijin/virtual_filesystem/memory.cpp
new file mode 100644
index 0000000..45d27e2
--- /dev/null
+++ b/source/mijin/virtual_filesystem/memory.cpp
@@ -0,0 +1,160 @@
+
+#include "./memory.hpp"
+
+#include "../io/stream.hpp"
+
+namespace mijin
+{
+std::vector<FileInfo> MemoryFileSystemAdapter::listFiles(const fs::path& folder)
+{
+    const detail::MemoryFolder* folderObj = findFolder(folder);
+    if (folderObj == nullptr)
+    {
+        return {};
+    }
+    std::vector<FileInfo> result;
+    result.reserve(folderObj->folders.size() + folderObj->files.size());
+
+    for (const auto& [name, subFolder] : folderObj->folders)
+    {
+        result.push_back(folderInfo(folder / name, subFolder));
+    }
+
+    for (const auto& [name, file] : folderObj->files)
+    {
+        result.push_back(fileInfo(folder / name, file));
+    }
+
+    return result;
+}
+
+FileInfo MemoryFileSystemAdapter::getFileInfo(const fs::path& file)
+{
+#if 0 // shouldn't be necessary
+    // empty means root
+    if (file.empty())
+    {
+        return {
+            .path = {},
+            .size = root_.folders.size() + root_.files.size(),
+            .exists = true,
+            .isFolder = true
+        };
+    }
+#endif
+
+    const detail::MemoryFolder* folderObj = findFolder(file.parent_path());
+    if (folderObj == nullptr)
+    {
+        return {};
+    }
+    const std::string filename = file.filename().generic_string();
+
+    if (auto itFolder = folderObj->folders.find(filename); itFolder != folderObj->folders.end())
+    {
+        return folderInfo(file, itFolder->second);
+    }
+    if (auto itFile = folderObj->files.find(filename); itFile != folderObj->files.end())
+    {
+        return fileInfo(file, itFile->second);
+    }
+    return {};
+}
+
+StreamError MemoryFileSystemAdapter::open(const fs::path& path, FileOpenMode mode, std::unique_ptr<Stream>& outStream)
+{
+    if (mode != FileOpenMode::READ)
+    {
+        return StreamError::IO_ERROR;
+    }
+
+    const detail::MemoryFolder* folderObj = findFolder(path.parent_path());
+    if (folderObj == nullptr)
+    {
+        return StreamError::IO_ERROR;
+    }
+
+    auto itFile = folderObj->files.find(path.filename().generic_string());
+    if (itFile == folderObj->files.end())
+    {
+        return StreamError::IO_ERROR;
+    }
+
+    std::unique_ptr<MemoryStream> stream = std::make_unique<MemoryStream>();
+    stream->openRO(itFile->second.data);
+    outStream = std::move(stream);
+
+    return StreamError::SUCCESS;
+}
+
+bool MemoryFileSystemAdapter::addFile(const fs::path& path, std::span<const std::uint8_t> data, Overwrite overwrite, CopyData copyData)
+{
+    detail::MemoryFolder& folder = *findFolder(path.parent_path(), true);
+    std::string filename = path.filename().generic_string();
+
+    if (folder.folders.contains(filename))
+    {
+        return false;
+    }
+
+    if (!overwrite && folder.files.contains(filename))
+    {
+        return false;
+    }
+
+    if (copyData)
+    {
+        data = fileData_.emplace_back(data.begin(), data.end());
+    }
+
+    folder.files.emplace(std::move(filename), detail::MemoryFile{.data = data});
+    return true;
+}
+
+void MemoryFileSystemAdapter::addFolder(const fs::path& path)
+{
+    (void) findFolder(path, true);
+}
+
+detail::MemoryFolder* MemoryFileSystemAdapter::findFolder(const fs::path& path, bool create) MIJIN_NOEXCEPT
+{
+    detail::MemoryFolder* folder = &root_;
+    for (const fs::path& part : path)
+    {
+        std::string partname = part.generic_string();
+        auto it = folder->folders.find(partname);
+        if (it == folder->folders.end())
+        {
+            if (!create)
+            {
+                return nullptr;
+            }
+            folder = &folder->folders[std::move(partname)];
+        }
+        else
+        {
+            folder = &it->second;
+        }
+    }
+    return folder;
+}
+
+FileInfo MemoryFileSystemAdapter::folderInfo(const fs::path& path, const detail::MemoryFolder& folder) const noexcept
+{
+    return {
+        .path = path,
+        .size = folder.folders.size() + folder.files.size(),
+        .exists = true,
+        .isFolder = true
+    };
+}
+
+FileInfo MemoryFileSystemAdapter::fileInfo(const fs::path& path, const detail::MemoryFile& file) const noexcept
+{
+    return {
+        .path = path,
+        .size = file.data.size(),
+        .exists = true
+    };
+}
+}
diff --git a/source/mijin/virtual_filesystem/memory.hpp b/source/mijin/virtual_filesystem/memory.hpp
new file mode 100644
index 0000000..b5c465d
--- /dev/null
+++ b/source/mijin/virtual_filesystem/memory.hpp
@@ -0,0 +1,55 @@
+
+#pragma once
+
+#if !defined(MIJIN_SOURCE_MIJIN_VIRTUAL_FILESYSTEM_MEMORY_HPP_INCLUDED)
+#define MIJIN_SOURCE_MIJIN_VIRTUAL_FILESYSTEM_MEMORY_HPP_INCLUDED 1
+
+#include <variant>
+#include <vector>
+
+#include "../container/vector_map.hpp"
+#include "../util/flag.hpp"
+#include "../virtual_filesystem/filesystem.hpp"
+
+namespace mijin
+{
+namespace detail
+{
+struct MemoryFile
+{
+    std::span<const std::uint8_t> data;
+};
+struct MemoryFolder
+{
+    VectorMap<std::string, MemoryFile> files;
+    VectorMap<std::string, MemoryFolder> folders;
+};
+}
+
+class MemoryFileSystemAdapter : public FileSystemAdapter
+{
+public:
+    MIJIN_DEFINE_FLAG(Overwrite);
+    MIJIN_DEFINE_FLAG(CopyData);
+private:
+    detail::MemoryFolder root_;
+    std::vector<std::vector<std::uint8_t>> fileData_;
+public:
+    [[nodiscard]] std::vector<FileInfo> listFiles(const fs::path& folder) override;
+    [[nodiscard]] FileInfo getFileInfo(const fs::path& file) override;
+    [[nodiscard]] StreamError open(const fs::path& path, FileOpenMode mode, std::unique_ptr<Stream>& outStream) override;
+
+    bool addFile(const fs::path& path, std::span<const std::uint8_t> data, Overwrite overwrite = Overwrite::NO, CopyData copyData = CopyData::NO);
+    bool addFile(const fs::path& path, std::span<const std::uint8_t> data, CopyData copyData)
+    {
+        return addFile(path, data, Overwrite::NO, copyData);
+    }
+    void addFolder(const fs::path& path);
+private:
+    detail::MemoryFolder* findFolder(const fs::path& path, bool create = false) MIJIN_NOEXCEPT;
+    FileInfo folderInfo(const fs::path& path, const detail::MemoryFolder& folder) const MIJIN_NOEXCEPT;
+    FileInfo fileInfo(const fs::path& path, const detail::MemoryFile& file) const MIJIN_NOEXCEPT;
+};
+} // namespace mijin
+
+#endif // !defined(MIJIN_SOURCE_MIJIN_VIRTUAL_FILESYSTEM_MEMORY_HPP_INCLUDED)