My apendice was removed by open method. Is it safe to make gimn musculation, abs? What about mountain bike, hills etc? The operation was in november 14.

Go for it. By now (10 weeks later) you should be fine. Usually it takes about 6 weeks to completely recover from a major surgery. Most patients are released to normal activity at 6 weeks from the surgery.
Gradually begin. I am not sure what you mean by gimn musculation, but let's get down to basics first, please know it should be okay to start riding your bike. I like low impact exercise at this stage. You will tire much more quickly, so be ready to scale back on the amount of riding. You must ease into abdominal muscle strain and exercise. Your muscleswill still be healing for some time.
Let me see it. Before a surgeon is capable of allowing the patient resume strenuous activity, it is imperative that the wound be examined postoperatively. Ultimately, there will be no restrictions at all. The duration of restriction typically ranges from 3 to 8 weeks.