Most elements in Flash have equivalents in HTML5 (and Adobe is working to add features to HTML to even out the differences.) This page gives some equivalencies between Flash components and HTML5 elements.
These are the elements created by selecting a graphic and choosing "Convert to Symbol".
Form button or link with images for each state
video element
audio element
div or other container element
img tag or CSS image
These are the user interface elements shipped as self-contained "component" objects.
Form checkbox or link w/ graphic (& logic)
Form radio button or link w/ graphic (& logic)
(Library: YUI, jQuery UI, etc.)
Text in page
option/select
Step control (HTML 5 forms)
Progress bar (HTML 5)
iframe
Range input type
textarea input type
text input type
(no direct equivalent)
Create element (e.g. Image), set src
Use iframe
Text in page
Text in page
Text field (in form)