Nikon Series E: 1979 top
Up through the 1970s Nikon only made very expensive professional lenses. Normal people had to buy discount brands lenses if they wanted something they could afford. Buying an off-brand lens was, and still is, the worst of all worlds: spending a lot on a camera, and then getting a dinky lens. The lens is the only part that affects the picture quality, so you are far better of with a crummy camera and good lenses.
To capture more of the amateur market Nikon decided to make a series of lenses called "Series E" which had great optical quality. They were built with well thought out, simple to manufacture optics and cheaper mechanics that were more than good enough for amateur use. These cheaper mechanics are often better than what Nikon makes today in some of their cheaper plastic AF lenses.
The optics are all great. Nikon only made Series E lenses in focal lengths and aperture ranges for which optics could be designed simply and still give great performance. For instance, I have the 100mm f/2.8E. A 100mm f/2.8 lens is very easy to make work very well for very little money. It is as sharp or sharper than my expensive 105mm f/2.8 AFD micro and 80-200mm f/2.8D AF-S especially at f/2.8. An 80-200mm f/2.8 zoom has to be expensive because it requires complex optics, but a fixed 100mm f/2.8 lens is easy to make inexpensively. Take these series E lenses very seriously.
The simplest Series E lenses were single-coated and others were multi-coated. Nikon's designers knew what they were doing: they used whatever they needed. The very simple classic designs of some of the fixed focal length Series E didn't need multi-coating.
The first Series E were a little bit ugly. The first were mostly black (lacking the chrome colored grab rings of the Nikkors) and used dorky big blocky nubs on the focus rings. In a few years Nikon updated the cosmetics and added the silver colored aluminum grab ring near the aperture ring and nicer looking nubs on the focus ring rubber, making them look very similar to the Nikkors.
These great lenses were never popular because Nikon was too honest.
Back then Nikon admitted that they used a little plastic here or there in the Series E lenses, which at the time was considered a crime. Remember everything is made of plastic today but back then everything was metal and weighed a ton. Nikon didn't use the Nikkor brand name because they were reserving the Nikkor brand only for what they considered professional lenses. Therefore everyone was afraid of the Series E lenses and few people bought them. Oddly, more people bought the crummier cheap brands that weren't as honest about what they were selling. Too bad, because the Series E were great lenses and far better than the discount ones. Today most Nikon AF lenses are far more cheaply made than the Series E were, and they are called Nikkor. Heck, even some of the super-expensive AF-S lenses have PLASTIC filter threads, and the Series E were solid metal.
From what I've seen Series E lenses typically had anodized black aluminum barrels and focus helicoids instead of enameled brass barrels and brass helicoids as the manual focus Nikkors do. All Series E had metal mounts, although some had plastic focus helicoids. They had aluminum zoom cams. Today's cheap AF Nikkors have plastic mounts and very little metal anywhere. The Series E have plastic aperture rings, a crime in their time but standard on almost every expensive Nikon lens today. The series E were very precisely made mechanically.
Some Series E optical designs were used in newer AF-Nikkor lenses. For instance, I read that the first 28mm f/2.8 AF and AF-D Nikkor sold up until about 2001 was the Series E five element design, and that the 70-210 f/4 AF was the 70-210 Series E design.
The Series E retained Nikon's superior seven-bladed diaphragms.
All Series E lenses are AI-s, and likewise fit every Nikon SLR camera, manual and auto focus. Some of the cheaper AF cameras and the D100 lose the ability to meter with the Series E as they do with all manual focus lenses.
See more about use on AF cameras here. The operation and compatibility of the Series E lenses is identical to the other manual focus AI-s lenses, which makes sense because they are AI-s.
In 2007, Nikon is re-using the E designation to refer to the electronic diaphragm of their PC-E lenses.
Nikkor Lens Technology