TransType has basically been developed to convert fonts that belong to the Mac operating system to Windows and vice-versa, thus if you're a user of both platforms this tool is a perfect solution to avoid incompatibilities.
Among the formats that it is capable of importing you will find FontLab VFB, Win Type 1 or Win TrueType / OpenType TT among others. As export formats you will have Win Type 1, Win TrueType, Mac Type 1, Mac TrueType suitcase, Mac TrueType dfont**, PC Multiple Master and Mac Multiple Master.
Are you a user of both platforms and you have compatibility problems with the fonts? Try out TransType and make sure that your fonts are compatible in Windows and Mac.