The best replacement for app.config is web.config.

The best alternatives to app.config are rated as following:
★★★★★  web.config
★★★★  settings
★★★★  exe.config
★★★  machine.config
★★★  user.config
★★  registry
★  settings.settings

Your alternative for app.config is not listed? Suggest!
Speaking about app.config, one probably shouldn't forget about class library.

Other search terms related to app.config and their ratings are:
★★★★★ class library
★★★★ exe
★★★ log4net
★ dll
You have in mind a companion for app.config and it is not yet here? Propose!



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app.config
web.config
settings