The "penultimate stage" refers to the second-to-last phase of a process. However, if you want to add more variety to your vocabulary, you may use different synonyms. For instance, you can use "preantepenultimate" to describe the stage that comes before the "antepenultimate," which is the third-to-last phase of a process. Alternatively, you can use "next-to-last," "second-to-final," or "almost at the end." You may also replace the word "stage" with "phase," "step," or "level." Alternatively, you may use idiomatic expressions such as "the end is in sight" to convey the same meaning. Adding more synonyms to your writing can enhance its readability and make it more enjoyable to read.