Open source software is readily and legally user modifiable. It is often (but not always) readily extensible - it can actually be quite difficult to extend in s

Open source software is readily and legally user modifiable. It is often (but not always) readily extensible - it can actually be quite difficult to extend in some cases. (There's plenty of difficult to work with spaghetti on GitHub.) Source available proprietary software is readily inspectable, but often not legal to modify (at least not for free). It might still be extensible (ex plugins) though! Closed source proprietary software is difficult to inspect, difficult to modify, and generally illegal to modify (for most use cases, in most jurisdictions). As above, it could easily be extensible though.