The plural of heir is heirs.
The plural of hair is hairs.
Also, your question is about which words have a plural form which is the same as the singular form. You aren't actually asking for which ones have "similar" forms. Arguably, "heir" and "heirs" are similar forms, wouldn't you say?
A quick rule of thumb for determining ...
Well in answer to your question and I am no expert on the plural forms of Greek words. All I was able to find is this
Adding the Ending s/es to Nouns and Verbs
The material below describes the rules of adding the ending s/es to the final consonants and vowels of nouns and verbs.
The ending s/es is added to nouns to form regular plural forms of nouns
I am not at all familiar with Greek, but this site says "Words ending in ές (es) turns into έδες (ethes)." So the plural would be "Herculethes"—but, being a proper name, it very well could be irregular.
In Latin, Hercules is third declension. The nominative plural is also "Hercules." This is what I would suggest as the most ...
This sounds like you are translating from a language that has a distinct word for the second person plural and uses it to express the difference between "thou" (singular) and "you-all" (plural).
English (at least standard semi-formal English) doesn't have this distinction. So it doesn't use it.
In English you would simply not use a ...
You would only say "these" if you had referred to more than one example.
You said that you have mentioned a singular platform, so you should say "other platforms like this".
The fact that 'platforms' is plural makes it clear that there are others like this one.