SQL Notebook is a free and open source Windows app written in C# for exploring and manipulating tabular data powered by a SQLite engine.
Ranked in these QuestionsQuestion Ranking
Pro Portable version
Pro Cross database queries
Any combination of data sources can be used together in the same SQL query, including cross-file, cross-database, and cross-server queries.
Pro Multi database
Microsoft SQL Server, PostgreSQL, and MySQL.
Free and open source.
Con Some queries do not work
Did some tests with PostgreSQL 9.5 and some complicated queries did not work.