LIXA, LIbre XA, is a free and open source XA transaction manager
...The client/server architecture of LIXA allows many application containers to share a single LIXA (state) server: this is ideal when horizontal scalability is a must and many identical application containers must refer to a single transactional environment.
LIXA can be used with the C, C++, Java, Python and COBOL programming languages.
Extended Server Pages (XSP/XSPD) for UNIX or Linux, C-based
XSP/XSPD high performance session based web application server for C/C++, Java and shell-scripts, requires UNIX/Linux based operating system, development of application programs like JSP's in C/C++, Java and/or shell scripts within same session context.
XappServer is an application server designed to make it easier for web application development in C++. If you are familiar with Java servlets, glassfish, and/or jboss, the learning curve in developing on XappServer should be shorter.
Photon provides very fast access to data containers (queues, maps, etc.) in shared memory - it can retrieve millions of data records per second. It also uses some RDB concepts like transactions and crash recovery. See web site for details.