SQL Relay http://sqlrelay.sourceforge.net/
From SQL Relay's home page:
SQL Relay is a persistent database connection pooling, proxying and load balancing system for Unix and Linux.
SQL Relay supports the following database backends:
SQL Relay includes a Tcl interface in the source distribution.
The documentation page [L1 ] provides this list:
"SQL Relay provides native client API's for many different programming languages."
Guides: C++ C Perl PHP Python Ruby Java References: C++ C Perl PHP Python Ruby Java
Tcl is not mentioned on the documentation page, despite being mentioned on the home page.