C3P0
c3p0 is an easy-to-use library for augmenting traditional (DriverManager-based) JDBC drivers with JNDI-bindable DataSources, including DataSources that implement Connection and Statement Pooling, as described by the jdbc3 spec and jdbc2 std extension.

Db Connection Broker
DbConnectionBroker is a pure Java package for handling multiple concurrent database connections. DbConnectionBroker creates a broker with a very simple interface for handing out and returning database connections from a configurable pool of connections. The Broker creates a dynamic pool of connections and manages them for you with a background housekeeping thread.

DBPool
A Java-based database connection pooling utility, which supports time-based expiry and statement caching, connection validation, and easy configuration using a pool manager. Also included is a generic object pool which can be extended to create your own pools of custom types.

DDConnectionBroker
"DDConnectionBroker" is a simple, light database connection-pooling tool for Java developers.

Jakarta DBCP
DBCP is a database connection pool that relies on code in the commons-pool package to provide the underlying object pool mechanisms that it utilizes.

Proxool
Proxool is a Java connection pool.