diff --git a/.gitignore b/.gitignore
index 17addf0..46dc322 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,7 @@
 *.o
 umka_shell
 umka_fuse
+umka_os
 mkdirrange
 mkfilepattern
 *.img
diff --git a/makefile b/makefile
index de18939..81c5bc4 100644
--- a/makefile
+++ b/makefile
@@ -6,7 +6,7 @@ CFLAGS_32=$(CFLAGS) -m32
 LDFLAGS=
 LDFLAGS_32=$(LDFLAGS) -m32
 
-all: umka_shell umka_fuse umka.sym umka.prp umka.lst tags tools/mkdirrange tools/mkfilepattern covpreproc default.skn skin.skn
+all: umka_shell umka_fuse umka_os umka.sym umka.prp umka.lst tags tools/mkdirrange tools/mkfilepattern covpreproc default.skn skin.skn
 
 covpreproc: covpreproc.c
 	$(CC) $(CFLAGS) $(LDFLAGS) $^ -o $@
@@ -17,6 +17,9 @@ umka_shell: umka_shell.o umka.o trace.o trace_lbr.o vdisk.o vnet.o lodepng.o pci
 umka_fuse: umka_fuse.o umka.o trace.o trace_lbr.o vdisk.o pci.o
 	$(CC) $(LDFLAGS_32) $^ -o $@ `pkg-config fuse3 --libs`
 
+umka_os: umka_os.o umka.o trace.o trace_lbr.o vdisk.o pci.o
+	$(CC) $(LDFLAGS_32) $^ -o $@
+
 umka.o umka.fas: umka.asm
 	INCLUDE="$(KOLIBRI)/kernel/trunk;$(KOLIBRI)/programs/develop/libraries/libcrash/trunk" $(FASM) $< umka.o -s umka.fas -m 1234567
 
@@ -62,6 +65,9 @@ umka_shell.o: umka_shell.c umka.h trace.h
 umka_fuse.o: umka_fuse.c umka.h
 	$(CC) $(CFLAGS_32) `pkg-config fuse3 --cflags` -c $<
 
+umka_os.o: umka_os.c umka.h
+	$(CC) $(CFLAGS_32) -c $<
+
 tools/mkdirrange: tools/mkdirrange.c
 	$(CC) $(CFLAGS) $(LDFLAGS) $< -o $@
 
@@ -71,5 +77,5 @@ tools/mkfilepattern: tools/mkfilepattern.c
 .PHONY: all clean
 
 clean:
-	rm -f *.o umka_shell umka_fuse umka.fas umka.sym umka.lst umka.prp coverage tools/mkdirrange tools/mkfilepattern
+	rm -f *.o umka_shell umka_fuse umka_os umka.fas umka.sym umka.lst umka.prp coverage tools/mkdirrange tools/mkfilepattern
 
diff --git a/umka_os.c b/umka_os.c
new file mode 100644
index 0000000..657f711
--- /dev/null
+++ b/umka_os.c
@@ -0,0 +1,106 @@
+#include <setjmp.h>
+#include <signal.h>
+#include <stdio.h>
+#include <sys/time.h>
+#include "umka.h"
+
+#define THREAD_STACK_SIZE 0x2000
+#define MAX_THREADS 16
+
+struct itimerval timeout = {.it_value = {.tv_sec = 0, .tv_usec = 999}};
+sigjmp_buf threads[MAX_THREADS], trampoline;
+size_t cur_thread = 0;
+size_t thread_cnt = 1;
+uint8_t stack_os[THREAD_STACK_SIZE];
+uint8_t stack_thrda[THREAD_STACK_SIZE];
+uint8_t stack_thrdb[THREAD_STACK_SIZE];
+
+static void add_new_thread(void (*func)(void), void *stack) {
+    if (!sigsetjmp(trampoline, 1)) {
+        __asm__ __inline__ __volatile__ (
+        "mov    esp, eax;"
+        "push   ecx"
+        :
+        : "a"(stack),
+          "c"(func)
+        : "memory");
+        if (!sigsetjmp(threads[thread_cnt++], 1)) {
+            longjmp(trampoline, 1);
+        } else {
+            __asm__ __inline__ __volatile__ (
+            "pop    ecx;"
+            "call   ecx"
+            :
+            :
+            : "memory");
+        }
+    }
+}
+
+void scheduler(int signo, siginfo_t *info, void *context) {
+    (void)signo;
+    (void)info;
+    (void)context;
+    printf("##### cur_thread: %u\n", cur_thread);
+    if (!sigsetjmp(threads[cur_thread], 1)) {
+        printf("##### saved\n");
+        cur_thread += 1;
+        if (cur_thread == thread_cnt) {
+            cur_thread = 0;
+        }
+        setitimer(ITIMER_PROF, &timeout, NULL);
+        siglongjmp(threads[cur_thread], 1);
+    }
+}
+
+void os() {
+    printf("0 osidle begin\n");
+    raise(SIGPROF);
+    while (1) { // osloop
+        for (int i = 0; i < 10000000; i++) ;
+        printf("0 osloop\n");
+        fflush(stdout);
+    }
+    printf("0 osidle end\n");
+}
+
+void thrda() {
+    printf("1 thrd a begin\n");
+    while (1) {
+        for (int i = 0; i < 10000000; i++) ;
+        printf("1 thrd a\n");
+        fflush(stdout);
+    }
+    printf("1 thrd a end\n");
+}
+
+void thrdb() {
+    printf("2 thrd b begin\n");
+    while (1) {
+        for (int i = 0; i < 10000000; i++) ;
+        printf("2 thrd b\n");
+        fflush(stdout);
+    }
+    printf("2 thrd b end\n");
+}
+
+int main() {
+    struct sigaction sa;
+
+    sa.sa_sigaction = scheduler;
+    sigemptyset(&sa.sa_mask);
+    sa.sa_flags = SA_SIGINFO;
+
+    if (sigaction(SIGPROF, &sa, NULL) == -1) {
+        printf("Can't install signal handler!\n");
+        return 1;
+    }
+
+//    add_new_thread(os,    stack_os[0x1000]);
+    add_new_thread(thrda, stack_thrda+THREAD_STACK_SIZE);
+    add_new_thread(thrdb, stack_thrdb+THREAD_STACK_SIZE);
+
+    os();
+
+    return 0;
+}