While there are several kinds of bonds, municipal bonds are among the most popular. A municipal bond is a government issued bond that is used to fun public services and planning, often being used to build roads and school, ports and airports and other forms of infrastructure. These bonds have recently been revitalized by new solutions utilizing technology to re-energize the system and make it more efficient. This has allowed for lower pricing and more accessibility for middle income investors where other binds might be too expensive. The trade of these bonds is far less restricted than generic stocks and are thus attractive to traders that wish to buy and sell their bonds more often, even as often buying and selling the same bond several times in a week.  
There are very clear and strict laws and regulations that cover how the money collected from the issuance of bonds and transactions are public and well-recorded, making these bonds attractive to the investor concerned with transparency and understanding of how their investment is being applied. They have competitive interest rates compared to similar alternatives, with an average interest rate somewhere around 4.5%. This consistency of return helps them to be a trusted and reliable place to invest over the long term.  
For the personal investor, municipal bonds are likely to always be a strong choice for investment, especially when the transparency of the issuer is of particular concern.