It is September 30, 2017. That's the last day of the current fiscal year for the federal government. After this, if a program hasn't received its official funding, it can't keep operating.
CHIP, the Children's Health Insurance Program, hasn't received funding reauthorization, a first since the program was started in 1997. It has received reauthorization a number of times and currently helps bring healthcare to millions of children. A recent bipartisan bill for reauthorization has been left hanging.
Also going away after today are a number of programs for hospitals that treat primarily poor people. The problem there is that since Obamacare was passed into law by Democratics, you have to buy health "insurance". So poor people do that, but almost always go for the "bronze plans", which carry the highest deductibles. When something serious happens and they end up in a hospital, the tab can run into the thousands.
Since the patients are poor, they can't pay. One way or the other, hospitals have to absorb the cost. The programs that are going away after tonight were designed to cushion the impact on hospitals.
Congress couldn't manage to come up with a health care plan to replace Obamacare, and they're doing nothing to address these problems.
Some of had hoped for better from them.