Not at this time, later, after, etc.
The best synonym for sometimes is occasionally. You can also say from time to time, now and then, periodically, intermittently.
There are not a lot of words to use instead of are, except other forms of "to be"--is, was, were. Normally you have to rewrite the sentence to find a more active verb. For example, my answer could be rewritten like this: Very few words exist that can replace are. Now the verbs in the sentence are "exist" and "replace." Sometimes it's difficult to avoid are, just like I did. I could rewrite the sentence again: Now I have used the verbs "exist" and "replace" instead of the "are." As long as you use mainly active verbs, an occasion are will not hurt your writing.
Alcohol
The noun animalcule is now known as microorganism
Assonance is the literary device used in the phrase "How are you now brown cow", where the similar vowel sounds of the words "now" and "brown" are repeated.
There are quite a few words that were used in old English that are almost the same as they are now, and some that have nearly the same spelling but a completely different meaning. For instance, Shoppe. Shoppe used to be the most common spelling of what we now spell Shop. On the other hand, Protest used to be mainly used to mean "Declare publicly", but now is primarily used to mean a "statement of disapproval". It is still spelled the same way. There are some words that were completely supplanted by other words. Onuppan is one such word, and it has been completely replaced with "Above".
Surgical glue is now often used instead of conventional stitches. It leave no marks, as stitches or staples do.
now
Other input devices are used, usually a mouse. In fact, before the mouse really caught on you pretty much only used to keyboard but now the mouse is used much more often seeing as the keyboard is generally only used for typing these days.
The words used in the Latin language were the words spoken by the ancient Romans and some of those words now have roots in the English language.
you have to now how to pronounce the words that are used in math