diff --git a/README.md b/README.md
index a6f6a46..9cbcecb 100644
--- a/README.md
+++ b/README.md
@@ -100,6 +100,8 @@ int main(int argc, char *argv[]) {
  * [apps/rust-hello](apps/rust-hello) Rust hello world program (note, the version of rust installed by brew on mac has issues, use the official rust installer from https://rust-lang.org/learn/get-started/)
  * [apps/zig-mandel](apps/zig-mandel) Zig ASCII mandelbrot generator program
  * [apps/zigtris](apps/zigtris) Zig Tetris (https://github.com/ringtailsoftware/zigtris)
+ * [apps/zigalloc](apps/zigalloc) Demonstration of using extram with zig allocator
+ * [apps/heap](apps/heap) Demonstration of `malloc()` on extram in C
 
 ## Quickstart (docker)
 
diff --git a/apps/Makefile b/apps/Makefile
index af42dd4..e5bbdb3 100644
--- a/apps/Makefile
+++ b/apps/Makefile
@@ -12,6 +12,7 @@ all:
 	(cd maze && make)
 	(cd heap && make)
 	(cd memtest && make)
+	(cd zigalloc && make)
 
 clean:
 	(cd sketch && make clean)
@@ -27,4 +28,5 @@ clean:
 	(cd maze && make clean)
 	(cd heap && make clean)
 	(cd memtest && make clean)
+	(cd zigalloc && make clean)
 
diff --git a/apps/zigalloc/Makefile b/apps/zigalloc/Makefile
new file mode 100644
index 0000000..43549f4
--- /dev/null
+++ b/apps/zigalloc/Makefile
@@ -0,0 +1,18 @@
+PROJECT=zigalloc
+TOPDIR=../..
+
+HEAP_SIZE=$(shell echo "1024 * 1024 * 8" | bc)
+HOST_EXTRA=-e ${HEAP_SIZE} -i 100000
+
+all:
+	@# zig's objcopy is broken, so use external tool
+	@# https://ziggit.dev/t/addobjcopy-producing-zero-padding-at-start-of-binary/13384
+	zig build -Dheapsize=${HEAP_SIZE} && ${PREFIX}objcopy zig-out/bin/${PROJECT} -O binary ${PROJECT}.bin
+
+clean: clean_common
+	rm -rf zig-out .zig-cache
+
+test: all
+	${TOPDIR}/hosts/host/host ${HOST_EXTRA} ${PROJECT}.bin
+
+include ${TOPDIR}/apps/makefile.common
diff --git a/apps/zigalloc/build.zig b/apps/zigalloc/build.zig
new file mode 100644
index 0000000..ee02aa0
--- /dev/null
+++ b/apps/zigalloc/build.zig
@@ -0,0 +1,56 @@
+const std = @import("std");
+const CrossTarget = @import("std").zig.CrossTarget;
+const Target = @import("std").Target;
+const Feature = @import("std").Target.Cpu.Feature;
+
+pub fn build(b: *std.Build) void {
+    var options = b.addOptions();
+    const heapsize = b.option(u32, "heapsize", "heap size in bytes") orelse 0;   // -Dheapsize=u32
+    options.addOption(u32, "heapsize", heapsize);
+
+    const features = Target.riscv.Feature;
+    var disabled_features = Feature.Set.empty;
+    var enabled_features = Feature.Set.empty;
+
+    // disable all CPU extensions
+    disabled_features.addFeature(@intFromEnum(features.a));
+    disabled_features.addFeature(@intFromEnum(features.c));
+    disabled_features.addFeature(@intFromEnum(features.d));
+    disabled_features.addFeature(@intFromEnum(features.e));
+    disabled_features.addFeature(@intFromEnum(features.f));
+    // except multiply
+    enabled_features.addFeature(@intFromEnum(features.m));
+
+    const target = b.resolveTargetQuery(.{
+        .cpu_arch = Target.Cpu.Arch.riscv32,
+        .os_tag = Target.Os.Tag.freestanding,
+        .abi = Target.Abi.none,
+        .cpu_model = .{ .explicit = &std.Target.riscv.cpu.generic_rv32},
+        .cpu_features_sub = disabled_features,
+        .cpu_features_add = enabled_features
+    });
+
+    const exe = b.addExecutable(.{
+        .name = "zigalloc",
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("src/main.zig"),
+            .target = target,
+            .optimize = .ReleaseSmall,
+        }),
+    });
+    exe.root_module.addOptions("buildopts", options);
+
+    b.installArtifact(exe);
+
+    exe.addAssemblyFile(b.path("../crt0.S"));
+    exe.setLinkerScript(b.path("../linker.ld"));
+    exe.addIncludePath(b.path("../../common"));
+
+    const bin = b.addObjCopy(exe.getEmittedBin(), .{
+        .format = .bin,
+    });
+    bin.step.dependOn(&exe.step);
+
+    const copy_bin = b.addInstallBinFile(bin.getOutput(), "zigalloc.bin");
+    b.default_step.dependOn(&copy_bin.step);
+}
diff --git a/apps/zigalloc/src/console.zig b/apps/zigalloc/src/console.zig
new file mode 100644
index 0000000..c5ae395
--- /dev/null
+++ b/apps/zigalloc/src/console.zig
@@ -0,0 +1,49 @@
+const std = @import("std");
+extern fn console_write(data: [*]const u8, len: usize) void;
+var wbuf:[4096]u8 = undefined;
+var cw = ConsoleWriter.init(&wbuf);
+const uvm = @import("uvm.zig");
+
+pub const WriteError = error{ Unsupported, NotConnected };
+
+pub const ConsoleWriter = struct {
+    interface: std.Io.Writer,
+    err: ?WriteError = null,
+
+    fn drain(w: *std.Io.Writer, data: []const []const u8, splat: usize) std.Io.Writer.Error!usize {
+        var ret: usize = 0;
+
+        const b = w.buffered();
+        uvm.print(b);
+        _ = w.consume(b.len);
+
+        for (data) |d| {
+            uvm.print(d);
+            ret += d.len;
+        }
+
+        const pattern = data[data.len - 1];
+        for (0..splat) |_| {
+            uvm.print(pattern);
+            ret += pattern.len;
+        }
+
+        return ret;
+    }
+
+    pub fn init(buf: []u8) ConsoleWriter {
+        return ConsoleWriter{
+            .interface = .{
+                .buffer = buf,
+                .vtable = &.{
+                    .drain = drain,
+                },
+            },
+        };
+    }
+};
+
+pub fn getWriter() *std.Io.Writer {
+    return &cw.interface;
+}
+
diff --git a/apps/zigalloc/src/main.zig b/apps/zigalloc/src/main.zig
new file mode 100644
index 0000000..d884980
--- /dev/null
+++ b/apps/zigalloc/src/main.zig
@@ -0,0 +1,18 @@
+const uvm = @import("uvm.zig");
+const console = @import("console.zig").getWriter();
+
+fn submain() !void {
+    try console.print("Hello world\n", .{});
+    try console.flush();
+
+    const foo = try uvm.allocator().dupe(u8, "copy me");
+    try console.print("dupe={s}\n", .{foo});
+    try console.flush();
+
+}
+
+export fn main() void {
+    _ = submain() catch {
+        uvm.println("Caught err");
+    };
+}
diff --git a/apps/zigalloc/src/uvm.zig b/apps/zigalloc/src/uvm.zig
new file mode 100644
index 0000000..15ae3ec
--- /dev/null
+++ b/apps/zigalloc/src/uvm.zig
@@ -0,0 +1,65 @@
+const uvm32 = @cImport({
+    @cDefine("USE_MAIN", "1");
+    @cInclude("uvm32_target.h");
+});
+const buildopts = @import("buildopts");
+const std = @import("std");
+
+const extram:[*]u8 = @ptrFromInt(uvm32.UVM32_EXTRAM_BASE);
+const extram_len = buildopts.heapsize;
+
+var fba:std.heap.FixedBufferAllocator = .init(extram[0..extram_len]);
+
+pub fn allocator() std.mem.Allocator {
+    return fba.allocator();
+}
+
+pub inline fn syscall(id: u32, param1: u32, param2: u32) u32 {
+    var val: u32 = undefined;
+    asm volatile ("ecall"
+        : [val] "={a1}" (val),
+        : [param1] "{a0}" (param1), [param2] "{a1}" (param2),
+          [id] "{a7}" (id),
+        : .{ .memory = true });
+    return val;
+}
+
+pub inline fn getc() ?u8 {
+    const key = syscall(uvm32.UVM32_SYSCALL_GETC, 0, 0);
+    if (key == 0xFFFFFFFF) {
+        return null;
+    } else {
+        return @truncate(key);
+    }
+}
+
+pub inline fn millis() u32 {
+    return syscall(uvm32.UVM32_SYSCALL_MILLIS, 0, 0);
+}
+
+// dupeZ would be better, but want to avoid using an allocator
+// this is of course, unsafe...
+var termination_buf:[128]u8 = undefined;
+
+pub inline fn print(m: []const u8) void {
+    @memcpy(termination_buf[0..m.len], m);
+    termination_buf[m.len] = 0;
+    const s = termination_buf[0..m.len :0];
+    _ = syscall(uvm32.UVM32_SYSCALL_PRINT, @intFromPtr(s.ptr), 0);
+}
+
+pub inline fn println(m: []const u8) void {
+    @memcpy(termination_buf[0..m.len], m);
+    termination_buf[m.len] = 0;
+    const s = termination_buf[0..m.len :0];
+    _ = syscall(uvm32.UVM32_SYSCALL_PRINTLN, @intFromPtr(s.ptr), 0);
+}
+
+pub inline fn yield() void {
+    _ = syscall(uvm32.UVM32_SYSCALL_YIELD, 0, 0);
+}
+
+pub inline fn putc(c:u8) void {
+    _ = syscall(uvm32.UVM32_SYSCALL_PUTC, c, 0);
+}
+
diff --git a/precompiled/memtest.bin b/precompiled/memtest.bin
new file mode 100755
index 0000000..f2ee777
Binary files /dev/null and b/precompiled/memtest.bin differ
diff --git a/precompiled/zigalloc.bin b/precompiled/zigalloc.bin
new file mode 100755
index 0000000..b70669c
Binary files /dev/null and b/precompiled/zigalloc.bin differ