Trebuchet Tk is a MUCK/MUSH/MOO GUI client written entirely in TCL/Tk. It supports both Unix/X11 and Windows, and includes powerful scripting, triggers, hilites, macros, quickbuttons, keybinds, etc. that you would expect from a good MU* client. It also supports MCP simple-edit, and GUI dialog packages for MOO and FBMUCK6. For Muck users, Trebuchet also supports intelligent colored editing of MUF and MPI programs.
e4Graph is a C++ library that allows programs to store graph-like data persistently and to access and manipulate that data efficiently. With e4Graph, you can arrange your data in the most natural form that reflects the relationships between its parts, rather than having to force it into a table-like format. The e4Graph library also allows you to concentrate on the relationships you want to represent, and not on how to store them in a database. You can modify data items, and add and remove connections and relationships between pieces of data on the fly. e4Graph allows you to represent an unlimited number of different connections between pieces of data, and your program can selectively manipulate the data according to the relationships it cares about, not having to know about other connections represented in the data set.
OpenIsis provides a library and tools to access CDS/ISIS databases, which are mostly used for bibliographic data (ISO2709, Z39.50) but also well suited for other catalogues due to the very flexible indexing mechanism. Based on a C library, there are also bindings for Perl and Java (Tcl to come).