Some languages like Chinese, Japanese, Korean, Thai, Khmer use writing systems that don't use spaces.
What are other such languages? Is there a list of these languages?
Korean does use spaces.
Lao and Burmese (Myanmar) don't use spaces.
Vietnamese uses spaces between syllables instead of between words (except some few recent loanwords).
Tibetan and Dzongkha use other marks to separate syllables rather than words and don't use spaces in the way that English or other languages use them.
Tai Lü - when written in the New Tai Lue script can be found written both without spaces between words and with spaces between syllabes.
Most minority languages written in the major Southeast Asian scripts (Burmese, Khmer, Lao, Thai) probably don't use spaces either, but I don't have details.
Minority Southeast Asian languages using their own native scripts (Tai Lue etc) might not use spaces, but I don't have details.
I believe scripts that had different final forms of letters, such as Greek and Hebrew used them to provide hints about word boundaries since spaces between words were not always consistently used in ancient times.
In the Old Ethiopic language Ge'ez a double dot (:) was used to separate words. The Modern Amkharic language of Ethiopia also uses the double dot, although spaces are now used increasingly.
The Nastaʿlīq form of Arabic calligraphy uses vertical arrangement to separate words. The beginning of each word is written higher than the end of the preceding word, so that a line of text takes on a sawtooth appearance. Nastaliq spread from Persia and today is used for Persian, Uyghur, Pashto, and Urdu.
You should clarify the question a bit to make sure you mean 'writing systems', not languages. Spoken language doesn't use spaces (or pauses) in the same way or same place as written language.
But more generally, space in writing is a recent invention to aid in ease of reading. The writing systems of Ancient Greek and Latin did not use spaces. Neither did those of Mesopotamian languages or Ancient Egyptian.
Vedic Sanskrit often has no spaces between the letters within a same sentence, with the exception of some signs, and modern Sanskrit has no spaces between the same parts of its compound.
Old Russian and Old Greek also used to avoid spaces between the words within a same phrase.