I will probably add to this as I go...
But you can click on the link to see a list of HTML Tags
from w3schools site (they are listed on the left side of the page when you get there)
<base>
This tag specifies the base URL and/or target for all relative URLs in a document.
It must have either an href or a target attribute present, or both.
There can only be one single <base> element in a document, and it must be inside the
<head> element.
<hr>
This tag defines a thematic break in an HTML page (e.g. a shift of topic).
It displays as a horizontal line.
<map>
This tag is used to define an image map. An image map is an image with clickable areas.
The required name attribute of the <map> element is associated with the <img>'s usemap
attribute and creates a relationship between the image and the map.
The <map> element contains a number of <area> elements, that defines the clickable areas
in the image map.
<pre>
Text in a <pre> element is displayed in a fixed-width font, and the text preserves both spaces
and line breaks. The text will be displayed exactly as written in the HTML source code.
<strong>
This element will display text as
bold and screen readers will recognise this.
There is also a <b> tag which will bold the text but screen readers may not recognise
this properly.
Also see my other page that shows some not used much Tags/Elements.
(or maybe they are, I haven't really decided yet)