A script that I literally use all the time. Despite it's old age it's a tool that I use on every single project because it lets you select everything in the scene based on similarities to your original object. Unlike the built-in "Select Similar" feature my script gives you compare options. For instance - most commonly I use it to compare mesh data (verts/face count) or size (bounding box). This is useful when you've collapsed mesh instancing or imported objects and need to compare the actual mesh to see if its "similar"
If you work in Arch-Viz or import geometry that comes in w/o instancing this script is most certainly for you.