Smalltalk implementation that's been powering mission critical business systems for three decades.
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Pros
Pro Scalable object-oriented persistence
Gemstone/S is a persistent object environment, capable of high performance database tasks.
Pro Free version even for commercial use
GemStone/S has very capable licenses for no cost that allow businesses to use it commercially for no cost.
Pro Extreme robustness, performance and flexibility
This product has a long line of evolution, guaranteeing all these qualities
Pro Smalltalk
Smalltalk is one of the most productive environments, which makes the hard things easy and the difficult, practical.
Pro Tightly related to Pharo Smalltalk
You can develop your Smalltalk projects on friendly Pharo and run them on the rock solid GemStone environment.
Pro Live debugging production errors
Never debug from textual traces anymore: do live debugging of saved stack traces for production errors
Cons
Con Vendor lock-in
The environment is unique and you easily become very dependent on what it has to offer, while there is no alternative vendor to switch to.