Proprietary tools exist at the whim of their creators - if they decide to discontinue a product, you're facing a dead-end. In particular, with proprietary tools that require activiation/validation (both initial, and throughout the time you're using them) you're at the mercy of the creators running the activation servers - if they shut these down, your tools suddenly stop working, or you'll be unable to reinstall them if you need to. Open Source tools aren't bound to a single "creator" - if the original project team are no longer interested in supporting or developing a tool, new people can take over. OS projects only die when *nobody* is interested in them any more - and even then, they can come back to life as soon as someone does take an interest.