Money Market Fund (MMF) is a financial instrument where managers take money from clients, invest it in bonds, bills, Real Estate etc and then give each client their interest. Once you've Invested in Money Market Fund, yours is to chill and wait for interest.
Once you've joined a specific MMF, you can deposit as low as Kshs. 100 in an MMF like safaricom's Mali, while other MMFs have set the minimal deposit range at Ksh 100.
The good thing about investing in an MMF is you can withdraw part or whole of your savings at any time, which makes MMFs ideal for keeping emergency funds.