Three new deals have brought JEMB Realty Corp.’s 1 Willoughby Square to nearly 50 percent leased. The new tenants will join FXCollaborative, the building’s architect and anchor tenant, in what is Brooklyn’s tallest office tower.

The highly diverse new arrivals are Propel, a fin-tech company, which will move from its previous Brooklyn offices to 10,000 square feet at 1 Willoughby; the Ms. Foundation for Women, a national social justice organization, taking 11,000 square feet; and nonprofit philanthropic group Walnut Ridge, in 5,000 square feet.

The 34-story, 500,000 square-foot tower is the first ground-up office project in downtown Brooklyn since a 2004 rezoning. Asking rents range from $69-$85 per square foot, except for the penthouse, which has not yet been priced.