Haworthia aff. sordida:

These plants were found in one of our friend's greenhouse with no label, yet bear strong resemblance to the very rare Haworthia sordida. According to a Haworthia expert we consulted, there is a population of sordida with elongated green leaves at Bluecliff Hills in South Africa that looks a lot like this plant. Without the original tag, it's impossible to say for certain what this plant is.