My contract explicitly states that I can't render services to another company. I would like to know if working on open source projects or freelancing count as such because I would like to work on some other projects without violating my contract. Freelancing might count as rendering services, but would open source work count too?
Yes it is counting. Before contacting a lawyer, I highly suggest you to discuss with your employer to negociate that right.
Most employers will see the value of you working in open source projects.
However, freelancing in the same industry may be a problem.
In any case, don't try to bypass the laws, talk with your employer first, then your lawyer if you can't get a written approval.