We present the results of the hierarchical clustering analysis of the Gaia DR2 data to search for clusters, co-moving groups, and other stellar structures within 3 kpc, increasing the number of identified structures to more than 8000. To aid in the analysis of the population properties, we developed a neural network called Auriga to robustly estimate the age, extinction, and distance of a stellar group based on the input photometry and parallaxes of the individual members. Many of the identified populations appear to be filamentary or string-like, and some span hundreds of parsec in length. Most of these string lack a central cluster, indicating that their filamentary structure is primordial, rather than the result of tidal stripping or dynamical processing. The youngest strings (<100 Myr) are orthogonal to the spiral arms, as they are currently defined. Examining the temporal structure of the spiral arms, we find that the Sagittarius arm has moved by ~1 kpc in the last 100 Myr, and the Perseus arm has been experiencing a relative lull in star formation activity over the last 25 Myr. Older populations trace several other arm-like structures that cannot be presently traced by dust and gas.