For schedule documentation, spreadsheets work fine: one worksheet describes use case delivery, while a second details design, implementation, and verification efforts for each object as they are identified. Once the initial schedule is developed, modifications take less than five minutes per week.
The design is documented in a System Architecture Specification (SAS). In addition to the architecture design, this document details public-member definition of all objects; the development environment, including tool list and installation instructions; design notes; diagnostics for quality assurance procedures; and performance monitoring. The SAS and SRD documents are the only two documents that need to be maintained throughout the product lifecycle. It is the go-to document for a maintenance programmer.
Design documents are notorious for being out of date with the actual implementation. This is avoided by using the SAS for a high-level view of the design, which includes the architecture and a description of each object. Detailed designs of complex individual objects and sequence diagrams for object identification should be documented separately. Designers then can discard these documents after peer reviews and implementation are complete.