NumFOCUS (the NumPy Foundation for Open Code for Usable Science) is a nonprofit founded to handle funds and act as a fiscal sponsor for many essential projects in the open source data science software stack, including several Sloan grantees. Projects choose to affiliate with NumFOCUS for mostly logistical reasons: lower overhead costs than universities; less-bureaucratic finance operations; and greater flexibility for operating across countries and organizations (e.g., hiring a research assistant at a third-party organization). The collection of so many open source projects under one umbrella, however, promises the opportunity to rapidly circulate best practices among member projects. One of the biggest issues shared across the NumFOCUS portfolio is project sustainability. Fund from this grant will help NumFOCUS build capacity in the areas of business planning and industry outreach to serve its portfolio of projects. Funding includes two years of support for a projects director, for efforts to build relationships with industry sponsors, for an annual workshop on business models and sustainability strategies for member projects, and to provide business plan and sustainability mentoring for projects that request it.