General replacements:
* Work: "The team put in a lot of work to finish the project."
* Labor: "The construction workers were exhausted after a day of hard labor."
* Exertion: "The climb to the summit required a great deal of exertion."
* Attempt: "She made several attempts to open the lock."
* Endeavor: "Their endeavor to build a better future for their children was admirable."
* Striving: "He was known for his striving to achieve excellence in all he did."
More specific replacements:
* Diligence: "She approached her studies with diligence, always prepared and focused."
* Determination: "His determination to succeed was evident in his unwavering commitment."
* Perseverance: "Despite the challenges, she persevered and ultimately achieved her goal."
* Industry: "The employees showed great industry, working tirelessly to meet the deadline."
* Application: "The students demonstrated a great deal of application in their research."
* Focus: "She brought a laser-like focus to her tasks, ensuring every detail was perfect."
* Commitment: "Their commitment to their cause was unwavering, driving them to make a difference."
* Passion: "Her passion for her work was contagious, inspiring others to excel."
Figurative language:
* Blood, sweat, and tears: "They poured blood, sweat, and tears into building the company."
* Herculean effort: "It took a Herculean effort to move the heavy boulder."
The best word to use will depend on the specific meaning you want to convey. Consider the tone of your writing and the context of the sentence when choosing a replacement for "effort."