Not much, I suppose.
If you have access to Brill, then the Chinese-English Dictionary Online contains the entries, among others, from Paul W. Kroll's A Student's Dictionary of Classical and Medieval Chinese. But randomly having access to Brill is one of the most rare things in the world though ($160 and that expires after five years of usage???)
Alternatively, if you have Pleco, you may purchase the same Kroll as a $40 add-on and browse it with ease in a native iOS or Android app. They also have the 漢語大詞典 for $50, which covers all the periods of the language including Classical, and the Gu Hanyu Da Cidian for $20, specifically aimed at Classical language.
If you are looking for a free source, consider the dictionary of ctext.org. If not much, it will at least provide the whole text of Kangxi dictionary definition in a digitized format, so if you already read Classical Chinese on a basic level, it will allow to get the general gist of things.
Personally, out of the non-Chinese language dictionaries of Classical Chinese, I am very partial to the dictionary attached to Kai Vogelsang's Introduction to Classical Chinese, so if there is any chance to (somehow, such as through institutional access) get hold of it, it would be probably a better option than all of the entries above. I mean, it contains the data that one generally expects from a language dictionary (such as Old Chinese pronuunciation, parts of speech, how the word combines with other words), which Classical Chinese dictionaries ordinarily neglect. Kroll is a helpful addition to that, but only an addition; its definitions are brief, and its stronger sides are just more characters and medieval usages.
Out of the Chinese-language dictionaries of Classical Chinese, then probably the 古漢語字典 by Wang Li would be the best option.