Nim vs Idris

There are generics, templates, macros in Nim. They can allow you to write new DSL for your application, or avoid all boilerplate stuff.

Checks your code at compile time.

With built-in "unittest" module you can create test with a very readable code.

Nim has a built-in VM, which executes macros and some other code at compile time. For example, you can check if you're on Windows, and Nim will generate code only for it.

Nim has "asyncdispatch" module, which allows you to write async applications.

The same code can be used for web, server, desktop and mobile.

Nim has a lot of common with Python in terms of syntax. Indentation-based syntax, for/while loops.

Imperative, OOP, functional programming in one language.

You can use Nim with any language that can be interfaced with C. There's a tool which helps you to create new C and C++ bindings for Nim - c2nim.
Also, you can use Nim with Objective C or even JavaScript (if you're compiling for these backends).

You don't need to deal with all those manual memory allocations, Nim can take care of it. But also you can use another GC, or tweak it for your real-time application or a game.

You only need to specify types in your procedures and objects - you don't need to specify type when you're creating a new variable (unless you're creating it without initialization).

You can use unicode names for variables, there is "unicode" module for operations with unicode.

writeLine(stdout, "hello") can be written as stdout.writeLine("hello")
proc add(a: int): int = a + 5 can be used like 6.add.echo or 6.add().echo()

Idris not only has support for type classes, but is a fully dependently typed language, giving you the full power to statically verify your code.

Because of full dependent types in Idris, the programmer can focus more on modelling the domain with types and waste less time fixing common bugs that the type checker will catch. Dependent types help apply type driven development and a lot of code auto generation, making the compiler and type checker an ally in developing working software instead of just getting in the way.