It probably isn't cash in a bank account. Balance sheets typically list "cash and cash equivalents", which can include short-term investments of various sorts.

The WMF balance sheet for 2015-16[1] shows that they held $46.7 million in cash and cash equivalents. Long term investments are listed as $11 million.

Fun trivia from their Statement of Activities[2]: they spent more on processing donations ($3.6m) and conferences/travel ($2.3m) than on hosting costs ($2m).

[1] https://upload.wikimedia.org/wikipedia/foundation/4/43/Wikim...

[2] What a for-profit company might call Income Statement or Profit & Loss.