ADT: Multiple instances of ADT commercial fire alarm installations (before it became Tyco Integrated Security), mostly in stores and other small installations.
EST: It seems like there aren’t that many EST systems in my area, but when I do see them, they are usually in an office building.
Fire-Lite: Very popular in small installs, such as stores, strip malls, and any other small to midsize building that would need a fire alarm system.
Gamewell/FCI: Can only think of one Gamewell/FCI system, they don’t really have a presence
Notifier: Is popular in small installations like Fire-Lite, but also has a presence in many large buildings (the Air Force Academy, for example, has Notifier systems in all of their buildings including very large class room buildings, and indoor arena, etc.)
Siemens (Cerberus Pyrotronics/Faraday): Has almost no presence where I live, can’t think of a single installation off of the top of my head
Silent Knight: Like Fire-Lite, is found in many smaller installations
Simplex: Has a very large presence in the educational market, as well as in many other large buildings. The two biggest colleges, as well as the 2-3 biggest school districts, have Simplex in most of their buildings (there are some exceptions, of course - my school, and one other school in my district have Notifier systems). The airport, them mall, multiple office buildings, etc. have Simplex systems as well.