I frequently hear people telling me about how wonderful their slow cookers (AKA "crock pot") are. In many cases they're right - meat that tends to come out tough in normal cooking comes out very tender from a slow cooker.
But do I really need a slow cooker to pull this off? It seems like such a basic concept - simmer and/or steam at low heat. What's so special about these devices? For kitchens with very limited space, can a slow cooker be "synthesized" from other cooking implements, or is there really no substitute?