Software Product Line Engineering (SPLE) is a prominent paradigm for the assembly of a family of products using product line core assets. The modeling of software assets that together form the actual products is critical for achieving the strategic benefits of Software Product Lines (SPLs). We propose a feature-based approach to software asset modeling based on abstractions provided by Domain-Specific Kits (DSKs). This approach involves a software Asset Metamodel (AMM) used to derive Asset Modeling Languages (AMLs) that define reusable software assets in domain-specific terms. The approach also prescribes a roadmap for modeling these software assets in conjunction with the product line reference architecture. Asset capabilities can be modeled using feature diagrams as the external views of the software assets. Internal views can be expressed in terms of Domain-Specific Artifacts (DSAs) with Variability Points (VPs), where the domain-specific artifacts are created using Domain-Specific Kits. This approach produces loosely coupled and highly cohesive software assets that are reusable for multiple product lines. The approach is validated by assessing software asset reuse in two different product lines in the finance domain. We also evaluated the productivity gains in large-scale complex projects, and found that the approach yielded a significant reduction in the total project effort.