Two freeware Commodore 64-style games comin' atcha.
Grand Mystic Quest of Discovery is a Flash-based puzzle platformer made by hulahulahest for the 19th Ludum Dare competition. You control a wizard in his quest to discover the secret of some ancient ruins. Learning spells gains you access to new areas, eventually allowing you to collect all six scroll pieces and find the exit. Due to the fact that it was made in 48 hours, the game contains no sound and has a somewhat disappointing ending, but the gameplay and pixel art graphics are solid. It takes about an hour to complete the game; your progress is saved automatically.
Rocky Memphis and the Temple of Ophuxoff is a downloadable platform game for Windows and Mac in which you guide the titular character through a large temple filled with monsters and treasure. The game presents you with the daunting task of collecting all 4000 pieces of treasure, which is done in a manner very similar to the gameplay in Jet Set Willy. Fortunately, a save function is available as well as an automatic mapper that keeps track of the rooms you've visited and completed, which makes things quite manageable and suitable for playing in short bursts. The level design and powerup placement appear to have been made with speedrunning in mind, so that should provide an extra challenge for those so inclined.