From what you described above what you want is continuous-computing. There are 2 sort of software on windows based platform that can provide what you are looking for. I'm not too familiar with any transactional log applications. With both the below HA/FT solutions, you could just use about any out there. ( just as long they run in windows )
Neverfail is a HA solution that protects your application from any data loss. In an event of a server outage, failover between both servers are seemless ( does not require human interaction) and depending on how much data is still left in the memory that isn't written to I/O on the Active server, the Passive Server will take over operations. This would provide you with close to 99.99% uptime.
Marathon is similar like Neverfail but it has an added protection which is component protection. With their FT feature, if any failure were to happen to your sever, like a disk failure or even a network failure, your application will keep on running. Thus no data loss or interruption to business.